Switchable solvents and methods of use thereof

ABSTRACT

A solvent that reversibly converts from a nonionic liquid mixture to an ionic liquid upon contact with a selected trigger, e.g., contact with CO 2 , is described. In preferred embodiments, the ionic solvent is readily converted back to the nonionic liquid mixture. The nonionic liquid mixture includes an amidine or guanidine or both, and water, alcohol, or a combination thereof. Single component amine solvents that reversibly convert between ionic and non-ionic states are also described. Some embodiments require increased pressure to convert; others convert at 1 atmosphere.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. s.119(e) ofprovisional patent application Ser. No. 60/781,336 filed Mar. 13, 2006,the contents of which is hereby incorporated by reference in itsentirety.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with Government support under DE-FG02-99ER14986contract awarded by the United States Department of Energy. TheGovernment has certain rights in the invention.

FIELD OF THE INVENTION

The field of the invention is solvents, and specifically solvents thatcan be reversibly converted between ionic and nonionic forms.

BACKGROUND OF THE INVENTION

Conventional solvents have fixed physical properties which can lead tosignificant limitations in their use as media for reactions andseparations. Many chemical production processes involve multiple stepssuch as reaction, separation, extraction and/or dissolution, and oftenthe type of solvent that is optimal for any one step is different fromthat which is optimal for the next step. Thus it is common for thesolvent to be removed after each step and a new solvent added inpreparation for the next step. This removal and replacement greatly addsto the economic cost and environmental impact of such processes.Therefore, there exists a need for a solvent that can change itsphysical properties.

Solvents are commonly used to dissolve material in manufacturing,cleaning, dyeing, extracting, and other processes. In order for asolvent to dissolve a material quickly, selectively, and in sufficientquantity, it is usually necessary for the solvent to have particularphysical properties. Examples of such properties include dielectricconstant, polarizability, acidity, basicity, viscosity, volatility,hydrogen-bond donating ability, hydrogen-bond accepting ability andpolarity. At some point in such a process after the dissolution,separation of the material from the solvent may be desired. Such aseparation can be expensive to achieve, especially if the solvent isnonvolatile as is commonly the case for polar solvents.

Moderate changes in temperature and pressure cannot be used as a methodfor dramatically changing solvent properties as they cause only minorchanges in a conventional solvent's physical properties. Somehigh-pressure fluids can be continuously and reversibly changed byvariations in pressure. Examples include supercritical fluids such asCHF₃ (Jessop, 1999), and CO₂-expanded liquids such as subcriticalmixtures of CO₂ and organic liquid (Subramaniam, 2002). A disadvantageof such fluids or liquids is the pressure required (greater than 25 barand often greater than 50 bar) causes added expense, inconvenience andrisk.

There is a need for liquids that are able to switch by application of atrigger from one form with a first set of physical properties to anotherform with a second and different set of physical properties.

SUMMARY OF THE INVENTION

In a first broad aspect, the invention provides switchable solvents andmethods of preparing and using such solvents. The solvents are based onamidine or guanidine and switch between a neutral form and a chargedform (amidinium or guanidinium) in response to selected trigger. Whenprepared as described hereinbelow, the charged form provides an ionicliquid below 100° C., e.g., at room temperature. The trigger to changefrom neutral form to charged form may be exposure of the neutral form toCO₂, CS₂, or COS. Given its convenience, CO₂ is especially preferred. Inpreferred embodiments, solvents of the invention are not onlyswitchable, but reversibly so, and removal of the trigger, e.g:,removing CO₂, causes the charged form to switch to the neutral form.

In a second broad aspect, the invention provides switchable solvents andmethods, of preparing and using such solvents, where the solvents arebased on amidine or guanidine and switch between a first form with nolocal charges and a second, zwitterionic form in response to selectedtrigger. The trigger to change from first form to second, zwitterionicform may be exposure of the first form to CO₂, CS₂, or COS. Given itsconvenience, CO₂ is especially preferred. Preferably, a solventaccording to this aspect of the invention is not only switchable, butreversibly so, and removal of the trigger, e.g., removing CO₂, causesthe second, zwitterionic form to switch to the first form.

It should be understood that it is appropriate for purposes of thepresent disclosure to call removal of a first trigger a “trigger”itself, in that it causes a change in properties of the compound inquestion.

An aspect of the invention is a solvent that is an ionic liquid whoseionic character is changed such that it becomes a nonionic liquid inresponse to a trigger. Another aspect of the invention is a solvent thatis a nonionic liquid whose nonionic character is changed such that itbecomes an ionic liquid in response to a trigger.

According to a further aspect, the invention provides an ionic liquidthat is formed by the reversible reaction of carbon dioxide with anamidine or guanidine and water. Reversibility has been observed asdescribed hereinbelow for both amidine and guanidine.

In one aspect, the invention provides an ionic liquid of formula (2)

-   -   where R is alkyl, alkenyl, alkynyl, aryl, silyl, or siloxyl, and        may be linear, branched, or cyclic, and may be substituted or        unsubstituted; R¹, R², R³, and R⁴ are independently H; a        substituted or unsubstituted C₁ to C₁₀ alkyl group that is        linear, branched, or cyclic; a substituted or unsubstituted        C_(n)Si_(m) group where n and m are independently a number from        0 to 10 and n+m is a number from 1 to 10; a substituted or        unsubstituted aryl group optionally containing one or more        {—Si(R⁶)₂—O—} units; or a substituted or unsubstituted        heteroaryl group optionally containing one or more {—Si(R⁶)₂—O—}        units; and R⁶ is a substituted or unsubstituted alkyl, aryl,        heteroaryl, or alkoxy moiety. In certain embodiments, R¹, R³,        and R⁴ are not hydrogen.

In another aspect, the invention provides an ionic liquid that is madeby a method comprising the steps of: mixing a compound with alcohol,water or a combination thereof, where the compound is of the formula(1):

-   -   where R¹, R², R³, and R⁴ are independently H; a substituted or        unsubstituted C₁ to C₁₀ alkyl group that is linear, branched, or        cyclic; a substituted or unsubstituted C_(n)Si_(m) group where n        and m are independently a number from 0 to 10 and n+m is a        number from 1 to 10; a substituted or unsubstituted aryl group        optionally containing one or more {—Si(R⁶)₂—O—} units; or a        substituted or unsubstituted heteroaryl group optionally        containing one or more {—Si(R⁶)₂—O—} units; and R⁶ is a        substituted or unsubstituted alkyl, aryl, heteroaryl, or alkoxy        moiety; contacting the mixture with carbon dioxide, CS₂, or COS;        and obtaining the ionic liquid. In certain embodiments, R², R³,        and R⁴ are not hydrogen.

In certain embodiments of the previous two aspects, the compound and thealcohol, water or combination thereof, are present in approximatelyequimolar amounts. In other embodiments, they are present innon-equimolar amounts.

In another aspect, the invention provides a method of making an ionicliquid, comprising the steps of: mixing a compound with alcohol, wateror a combination thereof where the compound is of the formula (1):

-   -   where R¹, R², R³, and R⁴ are independently H; a substituted or        unsubstituted C₁ to C₁₀ alkyl group that is linear, branched, or        cyclic; a substituted or unsubstituted C_(n)Si_(m) group where n        and m are independently a number from 0 to 10 and n+m is a        number from 1 to 10; a substituted or unsubstituted aryl group        optionally containing one or more {—Si(R⁶)₂—O—} units; or a        substituted or unsubstituted heteroaryl group optionally        containing one or more {—Si(R⁶)₂—O—} units; and R⁶ is a        substituted or unsubstituted alkyl, aryl, heteroaryl, or alkoxy        moiety; contacting the mixture with carbon dioxide; and        obtaining the ionic liquid.

The alcohol may be ROH, where R is alkyl, alkenyl, alkynyl, aryl, silyl,or siloxyl, and may be linear, branched, or cyclic, and may besubstituted or unsubstituted. The alcohol may be a primary or asecondary alcohol.

In another aspect, the invention provides a method of separating asolute from an alcoholic solution comprising the steps of: adding to analcoholic solution comprising a solute an amount of a compound offormula (1) that is about equimolar to the amount of alcohol in thealcoholic solution; contacting the resulting mixture with carbon dioxideto convert the mixture to a first component of ionic liquid and a secondcomponent of solute; and separating the first and second components toisolate the solute.

In a further aspect, the invention provides a method for separating adesired liquid from a mixture of an alcohol and the desired liquid,comprising the steps of: adding a compound of formula (1) to a mixtureof an alcohol and a desired liquid; contacting the mixture with carbondioxide to convert the alcohol and the compound to an ionic liquid; andseparating the ionic liquid and the desired liquid to isolate thedesired liquid, wherein the desired liquid is not reactive with thecompound in the presence of the carbon dioxide.

In another aspect, the invention provides a method for separating adesired liquid from a mixture of water and the desired liquid,comprising the steps of: adding a compound of formula (1) to a mixtureof water and the desired liquid; contacting the mixture with carbondioxide to convert the water and the compound to an ionic liquid; andseparating the ionic liquid and the desired liquid to isolate thedesired liquid, wherein the desired liquid is not reactive with thecompound in the presence of the carbon dioxide.

In another aspect, the invention provides a method for converting anionic liquid to a nonionic liquid, comprising the steps of: providing anionic liquid of formula (2), where R¹, R³, and R⁴ are not H, removingcarbon dioxide from the ionic liquid; and obtaining the nonionic liquid.Removing carbon dioxide may comprise one or more of: heating the ionicliquid, and contacting the ionic liquid with a nonreactive gas thatcontains insufficient CO₂, CS₂, or COS to sustain the ionic liquid inits ionic form, e.g., a nonreactive gas that contains substantially noCO₂, CS₂, or COS.

In a further aspect, the invention provides an ionic liquid having theformula (2), wherein the ionic liquid reversibly converts to a nonionicliquid when carbon dioxide is removed, and wherein the nonionic liquidconverts to the ionic liquid upon contact with carbon dioxide. Carbondioxide may be removed by contacting the ionic liquid with a gas thatcontains substantially no carbon dioxide. Carbon dioxide may be removedby contacting the ionic liquid with a nonreactive gas that containsinsufficient CO₂, CS₂, or COS to sustain the ionic liquid in its ionicform, such as, for example, a gas that contains substantially no CO₂,CS₂, or COS.

In yet a further aspect, the invention provides an ionic liquid offormula (4)

-   -   where R is alkyl, alkenyl, alkynyl, aryl, silyl, siloxyl, and        may be linear, branched, cyclic, and may be substituted or        unsubstituted; R¹, R², R³, R⁴, and R⁵ are independently H; a        substituted or unsubstituted C₁ to C₁₀ alkyl group that is        linear, branched, or cyclic; a substituted or unsubstituted        C_(n)Si_(m) group where n and m are independently a number from        0 to 10 and n+m is a number from 1 to 10; a substituted or        unsubstituted aryl group optionally containing one or more        {—Si(R⁶)₂—O—} units; or a substituted or unsubstituted        heteroaryl group optionally containing one or more {—Si(R⁶)₂—O—}        units; and R⁶ is a substituted or unsubstituted alkyl, aryl,        heteroaryl, or alkoxy moiety. In certain embodiments, R, R¹, R²,        R³, R⁴, and R⁵ are not hydrogen.

In a further aspect, the invention provides an ionic liquid that is madeby a method comprising the steps of: mixing a compound with an alcohol,water or a combination thereof, where the compound is of the formula(3):

-   -   where R¹, R², R³, R⁴ and R⁵ are independently H; a substituted        or unsubstituted C₁ to C₁₀ alkyl group that is linear, branched,        or cyclic; a substituted or unsubstituted C_(n)Si_(m) group        where n and m are independently a number from 0 to 10 and n+m is        a number from 1 to 10; a substituted or unsubstituted aryl group        optionally containing one or more {—Si(R⁶)₂—O—} units; or a        substituted or unsubstituted heteroaryl group optionally        containing one or more {—Si(R⁶)₂—O—} units; and R⁶ is a        substituted or unsubstituted alkyl, aryl, heteroaryl, or alkoxy        moiety; contacting the mixture with carbon dioxide, CS₂, or COS,        and obtaining the ionic liquid. In certain embodiments, R¹, R²,        R³, R⁴, and R⁵ are not hydrogen.

In certain embodiments of the previous two aspects, the compound and thealcohol, water or combination thereof, are present in approximatelyequimolar amounts. In other embodiments, they are present innon-equimolar amounts.

In another aspect, the invention provides a method of making an ionicliquid, comprising the steps of: mixing a compound with alcohol, wateror a combination thereof where the compound is of the formula (3):

-   -   where R¹, R², R³, R⁴, and R⁵ are independently H; a substituted        or unsubstituted C₁ to C₁₀ alkyl group that is linear, branched,        or cyclic; a substituted or unsubstituted C_(n)Si_(m) group        where n and m are independently a number from 0 to 10 and n+m is        a number from 1 to 10; a substituted or unsubstituted aryl group        optionally containing one or more {—Si(R⁶)₂—O—} units; or a        substituted or unsubstituted heteroaryl group optionally        containing one or more {—Si(R⁶)₂—O—} units; and R⁶ is a        substituted or unsubstituted alkyl, aryl, heteroaryl, or alkoxy        moiety; contacting the mixture with carbon dioxide; and        obtaining the ionic liquid.

The alcohol may be ROH, where R is alkyl, alkenyl, alkynyl, aryl, silyl,or siloxyl, and may be linear, branched, or cyclic, and may besubstituted or unsubstituted. The alcohol may be a primary or asecondary alcohol.

In another aspect, the invention provides a method of separating asolute from an alcoholic solution comprising the steps of: adding to analcoholic solution comprising a solute an amount of a compound offormula (3) that is about equimolar to the amount of alcohol in thealcoholic solution; contacting the resulting mixture with carbon dioxideto convert the mixture to a first component of ionic liquid and a secondcomponent of solute; and separating the first and second components toisolate the solute.

In another aspect, the invention provides a method for separating adesired liquid from a mixture of an alcohol and the desired liquid,comprising the steps of: adding a compound of formula (3) to a mixtureof an alcohol and a desired liquid; contacting the mixture with carbondioxide to convert the alcohol and the compound to an ionic liquid;separating the ionic liquid and the desired liquid to isolate thedesired liquid, wherein the desired liquid is not reactive with thecompound in the presence of the carbon dioxide.

In another aspect, the invention provides a method for separating adesired liquid from a mixture of water and the desired liquid,comprising the steps of: adding a compound of formula (3) to a mixtureof water and the desired liquid; contacting the mixture with carbondioxide to convert the water and the compound to an ionic liquid; andseparating the ionic liquid and the desired liquid to isolate thedesired liquid, wherein the desired liquid is not reactive with thecompound in the presence of the carbon dioxide.

In a further aspect, the invention provides a method for converting anionic liquid to a nonionic liquid, comprising the steps of: providing anionic liquid of formula (4) or an ionic liquid made from the compound offormula (3), where R, R¹, R², R³, R⁴, and R⁵ are not H, removing carbondioxide from the ionic liquid; and obtaining the nonionic liquid.Removing carbon dioxide may comprise one or more of: heating the ionicliquid, and contacting the ionic liquid with a nonreactive gas thatcontains insufficient CO₂, CS₂, or COS to sustain the ionic liquid inits ionic form, e.g., a nonreactive gas that contains substantially noCO₂, CS₂, or COS.

In a further aspect, the invention provides an ionic liquid having theformula (4), wherein the ionic liquid reversibly converts to a nonionicliquid when carbon dioxide is removed, and wherein the nonionic liquidconverts to the ionic liquid upon contact with carbon dioxide. Carbondioxide may be removed by contacting the ionic liquid with a gas thatcontains substantially no carbon dioxide. Carbon dioxide may be removedby contacting the ionic liquid with a nonreactive gas that containsinsufficient CO₂, CS₂, or COS to sustain the ionic liquid in its ionicform, such as, for example, a gas that contains substantially no CO₂,CS₂, or COS.

In yet a further aspect, the invention provides use of an ionic liquidof formula (2), (4) or (6), or made from a compound of formula (1), (3)or (5), as a sensor of CO₂, CS₂, or COS.

In a further aspect, the invention provides use of an ionic liquid offormula (2), (4) or (6), or made from a compound of formula (1), (3) or(5), as a detector of CO₂, CS₂, or COS.

In a further aspect, the invention provides use of an ionic liquid offormula (2), (4) or (6), or made from a compound of formula (1), (3) or(5), as a chemical switch.

In a further aspect, the invention provides use of an ionic liquid offormula (2), (4) or (6), or made from a compound of formula (1), (3) or(5), to conduct electricity.

In another aspect, the invention provides an ionic liquid of formula (6)

-   -   where R¹ and R² are independently a substituted or unsubstituted        C₁ to C₁₀ alkyl group that is linear, branched, or cyclic; a        substituted or unsubstituted C_(n)Si_(m) group where n and m are        independently a number from 0 to 10 and n+m is a number from 1        to 10; a substituted or unsubstituted aryl group optionally        containing one or more {—Si(R⁶)₂—O—} units; or a substituted or        unsubstituted heteroaryl group optionally containing one or more        {—Si(R⁶)₂—O—} units; and R⁶ is a substituted or unsubstituted        alkyl, aryl, heteroaryl, or alkoxy moiety.

In another aspect, the invention provides an ionic liquid that is madeby a method comprising the steps of: contacting a compound of formula(5) with carbon dioxide, CS₂, or COS:

R¹R²NH  (5)

where R¹ and R² are independently a substituted or unsubstituted C₁ toC₁₀ alkyl group that is linear, branched, or cyclic; a substituted orunsubstituted C_(n)Si_(m) group where n and m are independently a numberfrom 0 to 10 and n+m is a number from 1 to 10; a substituted orunsubstituted aryl group optionally containing one or more {—Si(R⁶)₂—O—}units; or a substituted or unsubstituted heteroaryl group optionallycontaining one or more {—Si(R⁶)₂—O—} units; and R⁶ is a substituted orunsubstituted alkyl, aryl, heteroaryl, or alkoxy moiety; and obtainingthe ionic liquid.

In certain embodiments of the previous aspect, at least one of R¹ and R²is lower alkyl. In one embodiment, R¹ is butyl and R² is ethyl.

In a further aspect, the invention provides a method of making an ionicliquid, comprising the steps of: contacting a compound of formula (5)with carbon dioxide:

R¹R²NH  (5)

where R¹, and R² are independently a substituted or unsubstituted C₁ toC₁₀ alkyl group that is linear, branched, or cyclic; a substituted orunsubstituted C_(n)Si_(n), group where n and m are independently anumber from 0 to 10 and n+m is a number from 1 to 10; a substituted orunsubstituted aryl group optionally containing one or more {—Si(R⁶)₂—O—}units; or a substituted or unsubstituted heteroaryl group optionallycontaining one or more {—Si(R⁶)₂—O—} units; and R⁶ is a substituted orunsubstituted alkyl, aryl, heteroaryl, or alkoxy moiety; and obtainingthe ionic liquid.

In another aspect, the invention provides a method of isolating a solutecomprising the steps of: adding a liquid compound of formula (5) to acomposition comprising a solute; contacting the mixture with carbondioxide to convert the mixture to at least a first component of ionicliquid and a second component of solute that is not soluble in the ionicliquid; and isolating the solute.

In another aspect, the invention provides a method for separating adesired liquid from a mixture comprising a compound of formula (5) andthe desired liquid, comprising the steps of: contacting the mixture withcarbon dioxide to convert the compound to an ionic liquid; andseparating the ionic liquid and the desired liquid to isolate thedesired liquid, wherein the desired liquid is not reactive with thecompound in the presence of the carbon dioxide.

In a further aspect, the invention provides a method for converting anionic liquid to a nonionic liquid, comprising the steps of: providing anionic liquid of formula (6), removing carbon dioxide from the ionicliquid; and obtaining the nonionic liquid.

In an embodiment of the previous aspect, removing carbon dioxidecomprises one or more of: heating the ionic liquid, and contacting theionic liquid with a nonreactive gas that contains insufficient carbondioxide to sustain the ionic liquid in its ionic form.

In another aspect, the invention provides an ionic liquid having theformula (6), wherein the ionic liquid reversibly converts to a nonionicliquid when carbon dioxide is removed, and wherein the nonionic liquidconverts to the ionic liquid upon contact with carbon dioxide. Carbondioxide may be removed by contacting the ionic liquid with a nonreactivegas that contains insufficient carbon dioxide to sustain the ionicliquid in its ionic form.

In another aspect, the invention provides a method of synthesizingpolymer comprising the steps of: adding monomer and initiator to aswitchable solvent in its nonionic state to form a solution; allowingthe monomer and initiator to react to form dissolved polymer insolution; contacting the solution with carbon dioxide to obtain ionicliquid in which the polymer is not soluble; and isolating the polymer. Anon-reactive solvent may be added to decrease viscosity of the mixture.

In certain embodiments, the previous aspect also comprises the step ofcontacting with carbon dioxide the ionic liquid from which polymer hasbeen isolated to restore the switchable solvent to the nonionic state.

The polymer produced may be polystyrene.

In certain embodiments, the switchable solvent is amidine and alcohol;amidine and water; amidine and alcohol and water; guanidine and alcohol;guanidine and water; guanidine and alcohol and water, primary amine;secondary amine; or tertiary amine. In some embodiments, the switchablesolvent is amidine and alcohol; amidine and water; or amidine andalcohol and water; and the amidine is a compound of formula (1). Inother embodiments the switchable solvent is guanidine and alcohol;guanidine and water; or guanidine and alcohol and water; and theguanidine is a compound of formula (3). In other embodiments, theswitchable solvent is an amine, preferably a secondary amine of formula(5).

In another aspect, the invention provides a polymer made by theforegoing methods. As used herein, “polymer” is intended to have a broadmeaning, and encompasses homopolymers, copolymers, terpolymers, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings.

FIG. 1 shows a chemical reaction equation and a schematic of thereaction. The chemical reaction equation shows DBU(1,8-diazabicyclo-[5.4.0]-undec-7-ene) and an alcohol on the left handside and amidinium alkyl carbonate on the right hand side. This reactioncan be reversed, as indicated. The schematic shows the same reactionwherein the nonpolar nonionic liquid mixture of DBU and the alcohol areon the left side under a blanket of N₂. The ionic liquid amidinium alkylcarbonate product is shown on the right side under a blanket of carbondioxide.

FIG. 2 graphically presents the polarity of nonionic liquid mixtures ofequimolar amounts of DBU and C3 to C10 alcohols in the lower curve (♦);and the polarity of the corresponding ionic liquids that result fromreaction of the liquid mixtures with CO₂ gas at 1 bar, in the uppercurve (▪). The polarity is indicated by the wavelength of maximumabsorbance of dissolved solvatochromic dye Nile Red.

FIG. 3 graphically presents the melting temperature of ionic liquidsthat are formed by the reaction of CO₂ with equimolar mixtures of DBUand C1 to C10 alcohols.

FIG. 4 shows a schematic of the miscibility test described in Example 2wherein decane is miscible with alcohol and DBU on the left side and isimmiscible with the corresponding ionic liquid, [DBUH⁺][RCO3⁻], on theright side. This separation is reversible as indicated.

FIG. 5A shows a chemical scheme ofN,N,N′,N′-tetramethyl-N″-phenylguanidine and water reversibly reactingwith carbon dioxide to form the corresponding guanidinium bicarbonate,which is an ionic liquid. FIG. 5B shows a chemical scheme ofN,N,N′,N′-tetramethyl-N″-(2-fluorophenyl)guanidine and water reactingwith carbon dioxide to form the corresponding guanidinium bicarbonate,which is also an ionic liquid. FIG. 5C shows a schematic of suchreactions as described in Example 3, wherein the guanidine in each case(denoted as “amine”) is miscible with wet ether on the left side, andthe guanidinium bicarbonate separates from the ether into the ionicliquid on the right side.

FIG. 6A shows a chemical scheme of Me-MTBD and alcohol reacting with CO₂to form the corresponding ionic liquid. FIG. 6B shows a chemical schemeof N,N,N′,N′-tetramethyl-N″-butylguanidine and methanol reacting withCO₂ to form the corresponding ionic liquid.

FIG. 7 shows NMR characterization data forN,N,N′,N′-tetramethyl-N″-phenylguanidine and its bicarbonate salt.

FIG. 8 shows an x-ray crystal structure of [DBUH][O₂COMe].

FIG. 9A shows a ¹H NMR spectrum of an equimolar solution of2-butyl-1,1,3,3-tetramethylguanidine and methanol. FIG. 9B shows thesame mixture after addition of CO₂ and subsequent protonation of the2-butyl-1,1,3,3-tetramethylguanidine and formation of the methylcarbonate anion. FIG. 9C shows a ¹H NMR spectrum of the mixture of FIG.9B after bubbling with nitrogen for 16 hours, indicating that the ionicliquid has reversed to its original components.

FIG. 10 graphically presents the change in conductivity of an equimolarmixure of methanol and 2-butyl-1,1,3,3-tetramethylguanindine inchloroform. The conductivity was switched on by bubbling the mixturewith CO₂ to form an ionic liquid; the conductivity was switched off byapplying heat (80° C.).

FIG. 11 graphically presents thermogravimetric analysis of2-butyl-1,1,3,3-tetramethylguanindinium methycarbonate. This graph plotsheat flow in milliwatts against temperature (° C.) and againstpercentage mass lost.

FIG. 12A graphically presents the change in conductivity of a neatDBU/hexanol mixture during CO₂ bubbling: three trials are presented toshow reproducibility. FIG. 12B graphically presents the change inconductivity of a neat tert-butanol/DBU mixture during CO₂ bubbling.

FIG. 13 graphically presents the change in conductivity over time forDBU/1-propanol, and DBU/1-propanol in THF.

FIG. 14A graphically presents the change in conductivity over time forDBU/1-hexanol in toluene with CO₂ bubbling. Two trials are presented toshow reproducibility. FIG. 14B graphically presents the change inconductivity over time for DBU/1-hexanol in toluene in the presence ofN₂.

FIG. 15 graphically presents conductivity of neat ethylbutylamine wherecarbon dioxide is added at room temperature (from 0 to 55 minutes), andwhere N₂ is added (from 55 to 100 minutes, 55° C.).

BRIEF DESCRIPTION OF THE TABLES

Tables 1-15 show the results of studies conducted as described in theworking examples, as follows:

Table 1. Miscibility of the [DBUH][O₂COR] ionic liquids with hexane,toluene and ethyl acetate (selected traditional nonpolar solvents);

Table 2. ¹³C{¹H} NMR chemical shifts of [DBUH][O₂COR] salts in CDCl₃;

Table 3. ¹³C{¹H} NMR chemical shifts of pure n-alcohols in CDCl₃;

Table 4. ¹H NMR chemical shifts of [DBUH][O₂COR] salts in CDCl₃;

Table 5. ¹H NMR chemical shifts of pure n-alcohols in CDCl₃;

Table 6. ¹H NMR chemical shifts for key protons observed in n-hexanol,DBU, and mixtures of n-hexanol and DBU;

Table 7. ¹H NMR spectroscopic data for amines and their carbamate salts;

Table 8. ¹³C NMR spectroscopic data for amines and their carbamatesalts;

Table 9. IR spectroscopic data for the carbamate salts of selectedsecondary amines;

Table 10. Comparison of polarities of ethylbutylamine and DBU/1-hexanolin ionic and nonionic forms to polarities of traditional solvents;

Table 11. Qualitative study of viscosity of secondary amines in thepresence and absence of CO₂;

Table 12. Wavelengths of secondary amines in the presence and absence ofCO₂;

Table 13. Miscibility of selected liquids in NHEtBu and its carbamatesalt;

Table 14. Solubility of selected solutes in NHEtBu and in its carbamatesalt; and

Table 15. Solubility of selected solutes in DBU/1-propanol mixture andin its alkylcarbonate salt.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, “aliphatic” refers to hydrocarbon moieties that arelinear, branched or cyclic, may be alkyl, alkenyl or alkynyl, and may besubstituted or unsubstituted. “Aryl” means a moiety including asubstituted or unsubstituted aromatic ring, including heteroarylmoieties and moieties with more than one conjugated aromatic ring;optionally it may also include one or more non-aromatic ring. Examplesof aryl moieties include, phenyl, biphenyl, naphthyl, anthryl,phenanthryl, pyrenyl, pyridyl, bipyridyl, xylyl, indolyl, thienyl, andquinolinyl.

As used herein “unsubstituted” refers to any open valence of an atombeing occupied by hydrogen. For example, a person of ordinary skill inthe art would understand that an unsubstituted C_(n)Si_(m) group is aC_(n)Si_(m)H_(x) group where n and m are independently a number from 0to 10, x is any number up to 2n+2m+2, and n+m is a number from 1 to 10.

“Substituted” means having one or more substituent moieties whosepresence does not interfere with the desired reaction. Examples ofsubstituents include alkyl, alkenyl, alkynyl, aryl, aryl-halide,heteroaryl, cyclyl (non-aromatic ring), Si(alkyl)₃, Si(alkoxy)₃, halo,alkoxyl, amino, amide, hydroxyl, thioether, alkylcarbonyl,alkylcarbonyloxy, arylcarbonyloxy, alkoxycarbonyloxy,aryloxycarbonyloxy, carbonate, alkoxycarbonyl, aminocarbonyl,alkylthiocarbonyl, phosphate, phosphate ester, phosphonato, phosphinato,cyano, acylamino, imino, sulfhydryl, alkylthio, arylthio,thiocarboxylate, dithiocarboxylate, sulfate, sulfato, sulfamoyl,sulfonamide, nitro, nitrile, azido, heterocyclyl, ether, ester,silicon-containing moieties, thioester, or a combination thereof.Preferable substituents are alkyl, aryl, heteroaryl, and ether. It isnoted that aryl halides are acceptable substituents. Alkyl halides areknown to be quite reactive, they are acceptable so long as they do notinterfere with the desired reaction.

As used herein, “heteroatom” refers to non-hydrogen and non-carbonatoms, such as, for example, O, S, and N.

“Alcohol” means a molecule of the formula ROH, where R is alkyl,alkenyl, alkynyl, aryl, silyl, or siloxyl, and may be linear, branched,cyclic, and may be substituted or unsubstituted. Substituents are asdefined above and include moieties that do not interfere with thedesired reaction. Alcohols for use in the invention may optionally bechiral.

The term “switched” means that the physical properties have beenmodified. “Switchable” means able to be converted from a first statewith a first set of physical properties to a second state with a secondset of physical properties. A “trigger” is a change of reactionconditions (e.g., introduction or removal of a gas) that causes a changein the physical properties. The term “reversible” means that thereaction can proceed in either direction (backward or forward) dependingon the reaction conditions.

“Short chain aliphatic” or “lower aliphatic” refers to C₁ to C₄aliphatic. “Long chain aliphatic” or “higher aliphatic” refers to C₅ toC₂₅ aliphatic. “DBU” means 1,8-diazabicyclo-[5.4.0]-undec-7-ene. As usedherein, “air that has had its carbon dioxide component substantiallyremoved” means that the air has insufficient carbon dioxide content tointerfere with the removal of carbon dioxide from the solution. For someapplications, untreated air may be successfully employed, i.e., air inwhich the carbon dioxide component is unaltered; this would provide acost saving.

As used herein, “amidine” (picture below) refers to a molecule with astructure R¹N═C(R²)—NR³R⁴, where R¹ through R⁴ are aliphatic or siloxylor aryl or aliphatic/siloxyl as discussed below. The bicarbonate salt ofan amidine (picture below) is termed an “amidinium bicarbonate”. Anamidinium salt that has the anionic counterion [ROCO₂ ⁻] is termed an“amidinium alkylcarbonate” (picture below). It should be noted thatamidine as used herein also includes the structure R¹N═CH—NR³R⁴ (i.e.,R² is replaced by H), where R¹, R³, and R⁴ are as discussed below.

As used herein, “guanidine” (picture below) refers to a molecule with astructure R¹N═C(NR²R³)(NR⁴R⁵) where R¹ through R⁵ are aliphatic orsiloxyl or aryl or aliphatic/siloxyl or aryl/siloxyl oraliphatic/aryl/siloxyl as discussed below. The bicarbonate salt of suchmolecule is termed the “guanidinium bicarbonate” (picture below). Aguanidinium salt that has the anionic counterion [ROCO₂ ⁻] is termed“guanidinium alkylcarbonate” (picture below).

“Ionic” means containing or involving or occurring in the form ofpositively or negatively charged ions, i.e., charged moieties.“Zwitterionic” means having two oppositely charged groups present atdifferent locations within the same molecule. For purposes of thisdisclosure, “ionic liquids” are salts that are liquid below 100° C.;such liquids are typically nonvolatile, polar and viscous. For purposesof this disclosure, “zwitterionic liquids” are zwitterionic compoundsthat are liquid below 100° C. “Nonionic liquids” means liquids that donot consist primarily of molecules with formal charges such as ions.Nonionic liquids are available in a wide range of polarities and may bepolar or nonpolar; they are typically more volatile and less viscousthan ionic liquids.

A polar molecule is a molecule in which some separation occurs of thecentres of positive and negative charge, generally resulting in a regionof partial positive charge and a region of partial negative charge.Polar solvents are typically characterized by a dipole moment. Ionicliquids are considered to be polar solvents (Aki, 2001; Reichardt,2005), even though a dipole may not be present, because they behave inthe same manner as polar liquids in terms of their ability to solubilizepolar solutes, their miscibility with other polar liquids, and theireffect on solvatochromic dyes. A polar solvent is generally better thana nonpolar (or less polar) solvent at dissolving polar or chargedmolecules.

“Nonpolar” means having weak solvating power of polar or charged solutemolecules. Nonpolar as used herein means devoid of polarity or havinglow polarity. Nonpolar solvents are associated with either having littleor no separation of charge, so that no positive or. negative poles areformed, or having a small or zero dipole moment. A nonpolar solvent isgenerally better than a polar solvent at dissolving nonpolar, waxy, oroily molecules.

“NMR” means Nuclear Magnetic Resonance. “Wet diethyl ether” meansdiethyl ether that has been purchased from a supplier and whosecontainer has been opened to the atmosphere such that water-from the airsurrounding the container has entered the solvent.

The invention provides a method of separating a solute (a dissolvedcompound) from solution by switching the physical properties (e.g.,polarity, volatility, conductivity, etc.) of the solvent of the system.When the solvent has been converted into its second form, the solute maybe separated from solution. Separation may include, for example,decanting, filtering, and centrifuging. The invention further provides amethod for maintaining or disrupting miscibility of two liquids by usinga reversible switchable solvent as one of the two liquids. When atrigger is applied, the switchable solvent's properties change and thenewly-immiscible liquids separate. An embodiment of the inventionprovides a switchable solvent that can be reversibly and readilyswitched between nonionic liquid and ionic liquid forms by applying orremoving CO₂, CS₂ or COS. In most of the discussion herein of suchembodiment and other embodiments of the invention, the term “CO₂” willbe employed though that gas may in some circumstances optionally bereplaced by CS₂ or COS, as discussed in more detail below.

In certain embodiments of the invention, the liquid mixture is (1)amidine and alcohol, (2) amidine and water, (3) amidine, alcohol andwater, (4) guanidine and alcohol, (5) guanidine and water, (6)guanidine, alcohol and water, (7) a mixture of one or more amidine andone or more guanidine and alcohol, water or a combination thereof, (8) anitrogen-containing organic compound that is of about equal or weakerbasicity than amidine (or guanidine) and alcohol, water or a combinationthereof, or (9) a primary, secondary or tertiary amine.

In some embodiments of the invention, it is desirable to have the amountof amidine, guanidine or combination thereof be greater than equimolarto the amount of alcohol, water or combination thereof so that, uponexposure of the liquid mixture to CO₂ and after conversion of much ofthe liquid to ionic liquid, there remains some amidine, guanidine orcombination thereof in non-ionic form. Having such remaining non-ioniccomponent(s) in the liquid confers a practical advantage such as reducedviscosity, preferred pH, or different phase behaviour, relative to otherstoichiometry (equimolar or excess alcohol, water or combinationthereof).

In other embodiments of the invention, it is desirable to have theamount of amidine, guanidine or combination thereof be less thanequimolar to the amount of alcohol , water or combination thereof sothat, upon exposure of the liquid mixture to CO₂ and after conversion toionic liquid, there remains some alcohol, water or combination thereofin non-ionic form. Similarly to the above-described embodiments, havingsuch remaining non-ionic component(s) in the liquid confers a practicaladvantage such as reduced viscosity, preferred pH, or different phasebehaviour, relative to other stoichiometry (equimolar or excess amidine,guanidine or combination thereof).

Even in applications where the intention is to have an equimolar mixtureof amidine, guanidine or combination thereof and alcohol, water orcombination thereof, it may not be necessary or practical for themixture to be precisely equimolar. While having the mixture be exactlyequimolar would allow the greatest change in physical properties uponexposure of the mixture to CO₂, a large change in physical propertieswill still be obtained with mixtures that moderately deviate fromequimolar. The larger the deviation from equimolar, the smaller theexpected change in physical properties of the liquid upon exposure toCO₂.

An amidine is depicted below,

-   -   where R¹, R², R³, and R⁴ are independently H; a substituted or        unsubstituted C₁ to C₁₀ alkyl group that is linear, branched, or        cyclic; a substituted or unsubstituted C_(n)Si_(m) group where n        and m are independently a number from 0 to 10 and n+m is a        number from 1 to 10; a substituted or unsubstituted aryl group        optionally containing one or more {—Si(R⁶)₂—O—} units; a        substituted or unsubstituted heteroaryl group optionally        containing one or more {—Si(R⁶)₂—O—} units; and    -   R⁶ is a substituted or unsubstituted alkyl, aryl, heteroaryl, or        alkoxy moiety; wherein a substituent is independently alkyl,        alkenyl, alkynyl, aryl, aryl halide, heteroaryl, non-aromatic        rings, Si(alkyl)₃, Si(alkoxy)₃, halo, alkoxy, amino, ester,        amide, thioether, alkylcarbonate, phosphine, thioester, or a        combination thereof.

In the presence of an alcohol and carbon dioxide, such an amidineconverts to an amidinium alkylcarbonate as depicted below,

-   -   where R where R is alkyl, alkenyl, alkynyl, aryl, silyl,        siloxyl, and may be linear, branched, cyclic, and may be        substituted or unsubstituted; R¹, R², R³, and R⁴ are as defined        above.

In the presence of water and carbon dioxide, such an amidine converts toan amidinium bicarbonate as depicted below,

where R¹, R², R³, and R⁴ are as defined above. In the case of DBU andwater in the presence of CO₂, solid bicarbonate forms.

A guanidine is as shown below,

-   -   where R¹, R², R³, R⁴ and R⁵ are independently H; a substituted        or unsubstituted C₁ to C₁₀ alkyl group that is linear, branched,        or cyclic; a substituted or unsubstituted C_(n)Si_(m) group        where n and m are independently a number from 0 to 10 and n+m is        a number from 1 to 10; a substituted or unsubstituted aryl group        optionally containing one or more {—Si(R⁶)₂—O—} units; a        substituted or unsubstituted heteroaryl group optionally        containing one or more {—Si(R⁶)₂—O—} units;    -   R⁶ is a substituted or unsubstituted alkyl, aryl, heteroaryl, or        alkoxy moiety;    -   wherein a substituent is independently alkyl, alkenyl, alkynyl,        aryl, aryl halide, heteroaryl, non-aromatic rings, Si(alkyl)₃,        Si(alkoxy)₃, halo, alkoxy, amino, ester, amide, thioether,        alkylcarbonate, phosphine, thioester, or a combination thereof.

In the presence of an alcohol and carbon dioxide, such a guanidineconverts to a guanidinium alkylcarbonate as depicted below,

-   -   where R is alkyl, alkenyl, alkynyl, aryl, silyl, siloxyl, and        may be linear, branched, cyclic, and may be substituted or        unsubstituted; and R¹, R², R³, R⁴ and R⁵ are as defined above.

In the presence of water and carbon dioxide, such a guanidine convertsto an guanidinium bicarbonate as depicted below,

where R, R¹, R², R³, R⁴, and R⁵ are as defined above.

A reversibly switchable liquid solvent was formed by reacting theguanidine base N,N,N′,N′-tetramethyl-N″-phenylguanidine with carbondioxide in the presence of water (see the reaction scheme below, andExample 3). The complete reverse reaction was effected by bubbling withN₂, and it was verified by ¹H NMR that no bicarbonate remained (see FIG.7).

Analogously, a switchable solvent was converted by reacting theguanidine base N,N,N′,N′-tetramethyl-N″-(2-fluorophenyl)guanidine withcarbon dioxide in the presence of water (see the reaction scheme below,FIG. 5 and Example 3).

Another reversibly switchable ionic liquid was formed at roomtemperature by exposing an equimolar mixture of methanol and2-butyl-1,1,3,3-tetramethylguanidine (see below where R=butyl) togaseous CO₂ at one atmosphere. Reversibility of this system wasdemonstrated by Nuclear Magnetic Resonance (¹H and ¹³C) and conductivitystudies (see FIGS. 9 and 10) as described in Example 4B. Formation ofthe ionic liquid occurred after bubbling CO₂ through a 1:1 molar ratiomixture of 2-butyl-1,1,3,3-tetramethylguanidine and methanol for 20minutes. The ionic liquid was then converted back to2-butyl-1,1,3,3-tetramethylguanidine and methanol by bubbling with N₂ orargon overnight; the ionic liquid can also be reversed solely by heat,as indicated by thermogravimetric studies (see FIG. 11). The ionicliquid underwent reversal at temperatures as low as 50° C., releasingCO₂ and low-boiling methanol. This system is suitable for applicationswhere removal of the alcohol by evaporation is desirable after switchingto the guanidine and alcohol.

Amines employed as single component systems are also suitable asswitchable solvents. Primary and secondary amines are preferred;secondary amines are particularly preferred. Such systems, relative toDBU/ROH systems, generally have decreased sensitivity to moisture.Single component systems are attractive due to cost effectiveness,decreased number of components for undesired side reactions, andconvenient operation in industrial applications. The reaction of primaryamines together with DBU and CO₂ and has recently been investigated byWeiss's research group and is described in Yamada et al. (2007).

Referring to the single component amine system of the present invention,a scheme depicting the reversible switching of secondary amines in thepresence of CO₂ is provided below.

-   -   where R¹ and R² are independently a substituted or unsubstituted        C₁ to C₁₀ alkyl group that is linear, branched, or cyclic; a        substituted or unsubstituted C_(n)Si_(m) group where n and m are        independently a number from 0 to 10 and n+m is a number from 1        to 10; a substituted or unsubstituted aryl group optionally        containing one or more {—Si(R⁶)₂—O—} units; or a substituted or        unsubstituted heteroaryl group optionally containing one or more        {—Si(R⁶)₂—O—} units; and R⁶ is a substituted or unsubstituted        alkyl, aryl, heteroaryl, or alkoxy moiety.

Tertiary amines may be switched once (from nonionic to ionic) but ingeneral are not suited to reversibility as they lack an N—H bond intowhich CO₂ can be inserted. Although primary amines give solid carbamatesalts at room temperature, they are well suited to serve as switchablesolvents at higher temperatures where their carbamate salts are liquid.Secondary amines are particularly preferred as reversibly switchablesolvents as there are many examples of secondary amines with nonionicand ionic forms that are liquid at room temperature. However, ingeneral, secondary amines have some toxicity and would not be suitablefor use as solvents, for example, for food preparation.

N-butyl-N-ethylamine (NHEtBu) is an exemplary switchable solvent thatuses the same benign triggers as amidine and/or guanidine/alcoholmixtures. Unlike such mixtures, NHEtBu is water-insensitive, is lessexpensive than amidines, and has a significantly less polar low-polarityform.

NHEtBu is used as a model for many of the secondary amine studiesdescribed herein. It is a switchable solvent that switches from very lowpolarity when under air to much higher polarity when CO₂ is bubbledthrough it. The polar form is believed to be primarily the carbamatesalt (N,N-butylethyl-ammonium N′,N′-butylethylcarbamate), although inthe presence of water there may be some bicarbonate salt. Initialexperiments with secondary amines show that the presence of moisturedoes not interfere with the switchable reaction unless there is a verylarge amount of water such as one mole of water per mole of amine. Ifthere is a large amount of water, a white solid is obtained whichappears, by spectroscopy, to be the bicarbonate salt.

Studies were conducted using NHEtBu and carbon dioxide to reversiblyform an ionic liquid. Various solids were tested for their solubility inNHEtBu and its carbamate salt (see Table 14). Particulary low polaritysolids were soluble in only NHEtBu, while solids of higher polarity wereeither soluble in both or only soluble in the carbamate. Solids of veryhigh polarity or hydrophilicity were soluble in neither form. Variousliquids, including toluene, mesitylene, propylene carbonate, styrene,decane, 5-trans-decene, hexadecane and water, were found to be misciblewith both NHEtBu and its carbamate salt (see Table 13). Stilbene, incontrast, was miscible with NHEtBu and immiscible with the carbamate.

Conductivity of NHEtBu was studied in the presence of CO₂ and N₂;results are depicted in FIG. 15. A small amount of water in NHEtBu doesnot impede its reversibility. An equimolar amount of water in NHEtBuresults in creation of solid bicarbonate salt when CO₂ is bubbledthrough the mixture. Confirmation of the identification of the whiteprecipitate was obtained from its IR peak at 836 cm⁻¹ (bicarbonateout-of-plane vibration).

Polarities of secondary amines in their amine and carbamate forms weredetermined using the solvatochromic probe Nile Red and are reported aswavelength values (λ, nm). As shown in Table 12, NHEtBu has a very lowpolarity, lower than that of ethyl acetate, but after conversion of theamine to the carbamate the polarity rises to become comparable toacetone. The viscosity also visibly increases during the CO₂ treatmentas seen in Table 11. Bubbling nitrogen through the carbamate ionicliquid for 2.5 h converted it back to low polarity again, as shown bythe (reformed) nonionic liquid's wavelength value.

N-benzylmethylamine (NHBzMe) is a significantly more polar secondaryamine than NHEtBu. Otherwise it behaves similarly; CO₂ exposure causedan increase in polarity and viscosity while treatment with N₂ at 60° C.reversed that change. The final λ_(max) is slightly higher (536 nm) thanthe original value for NHBzMe before exposure to CO₂. The two forms ofNHBzMe almost exactly match the polarities of the two forms ofDBU/1-hexanol.

Secondary amines or protonated secondary amines may react with aldehydesor ketones to create iminium cations, a reaction that is not possible inthe amidine/ROH or guanidine/ROH switchable solvents. In mostapplications of switchable solvents, such reactivity is undesirable.However, in some applications it can be advantageous, for example,reactions of unsaturated aldehydes that are promoted by iminium cationformation (see Jen et al. 2000).

Secondary amines that are volatile (i.e., having boiling points belowabout 100° C.) will suffer evaporative losses during the switching offprocess. That is, the use of heat and/or flushing gas to flush away theCO₂ will also cause a significant portion of the secondary amine toevaporate. For this reason, less volatile secondary amines arepreferred.

Referring to FIG. 1, a chemical scheme and schematic drawing are shownfor a switchable solvent system of the amidine DBU and an alcohol (seeExample 1).

FIG. 2 graphically depicts the polarity of the nonionic liquid mixturesof DBU and C1 to C10 n-alcohols and the ionic liquids formed afterexposure to carbon dioxide. The graph in FIG. 2 conveys polarity bydisplaying the wavelength of maximum absorbance of dissolvedsolvatochromic dye Nile Red for each system. A larger wavelengthindicates greater polarity of the system.

FIG. 3 shows the melting temperature of ionic liquids formed by reactingCO₂ with equimolar mixtures of DBU with n-alcohols of varying lengths ofcarbon chains, as indicated.

FIG. 4 shows a schematic of the miscibility of decane with the nonionicand ionic forms of DBU and alcohol. The nonionic liquid mixture ismiscible with decane. The ionic liquid is immiscible with decane. Thisseparation is reversible as indicated. The same behaviour was observedwith hexane in place of decane for a DBU/alcohol system. It was observedthat the chosen alcohol must not have too long an alkyl chain, or suchseparation will not be observed; the alcohol's alkyl chain must beshorter than 10 carbons for the ionic form to be immiscible with hexane.

FIG. 5A shows a chemical scheme ofN,N,N′,N′-tetramethyl-N″-phenylguanidine and water reacting with carbondioxide to form the corresponding guanidinium bicarbonate. FIG. 5B showsa chemical scheme of N,N,N′,N′-tetramethyl-N″-(2-fluorophenyl)guanidineand water reacting with carbon dioxide to form the correspondingguanidinium bicarbonate. A schematic at FIG. 5C depicts the experimentdescribed in Example 3 where the guanidine and wet diethyl ether reactwith carbon dioxide to form a liquid ionic salt at the bottom of thevessel and diethyl ether at the top of the vessel, under a blanket ofCO₂. This reaction is not reversible by the simple application of N₂ orargon.

FIG. 6A shows a chemical scheme of1,3,4,6,7,8-hexahydro-1-methyl-2H-pyrimido [1,2-a] pyrimidine “Me-MTBD”in alcohol reacting with CO₂ to form the corresponding salt(1,3,4,6,7,8-hexahydro-1-methyl-2H-pyrimido [1,2-a] pyrimidiniumhexylcarbonate). This reaction is not reversible by the simpleapplication of heat. FIG. 6B shows a chemical scheme ofN,N,N′,N′-tetramethyl-N″-butylguanidine and methanol reacting with CO₂to form the corresponding ionic liquid.

FIG. 7 shows NMR characterization data forN,N,N′,N′-tetramethyl-N″-phenylguanidine and its bicarbonate salt.

FIG. 8 shows an x-ray crystal structure of [DBUH][O₂COMe]. Details ofthe data collection are provided in Example 9. This structure isprovided as further proof of the structure of the salt that is formed bybubbling CO₂ through a mixture of DBU and alcohol. Methanol was used forthe formation of the studied crystal since CO₂ in a DBU/MeOH systemproduces a salt in solid form.

FIG. 9A shows a ¹H NMR spectrum of an equimolar solution of2-butyl-1,1,3,3-tetramethylguanidine and methanol. FIG. 9B shows thesame mixture after addition of CO₂ and subsequent protonation of the2-butyl-1,1,3,3-tetramethylguanidine and formation of the methylcarbonate anion. FIG. 9C shows a ¹H NMR spectrum of the mixture of 9Bafter bubbling with nitrogen for 16 hours, indicating that the ionicliquid has reversed to its original components.

FIG. 10 graphically presents the change in conductivity of an equimolarmixure of methanol and 2-butyl-1,1,3,3-tetramethylguanindine inchloroform. The conductivity was switched on by bubbling the mixturewith CO₂ to form an ionic liquid; the conductivity was switched off byapplying heat (80° C.).

FIG. 11 graphically presents thermogravimetric analysis of2-butyl-1,1,3,3-tetramethylguanindinium methycarbonate. This graph plotsheat flow in milliwatts against temperature (° C.) and againstpercentage mass lost. This graph indicates that a percentage of mass waslost from the sample that is consistent with loss of CO₂ and methanol.The mass loss began at aproximately 50° C.

FIG. 12A graphically presents the change in conductivity of a neatDBU/hexanol mixture during CO₂ bubbling. Three trials are presented toshow reproducibility. FIG. 12B graphically presents the change inconductivity of a neat tert-butanol/DBU mixture during CO₂ bubbling.

FIG. 13 graphically presents the change in conductivity over time forDBU/1-propanol, and DBU/1-propanol in THF.

FIG. 14A graphically presents the change in conductivity over time forDBU/1-hexanol in toluene with CO₂ bubbling. Two trials are presented toshow reproducibility. FIG. 14B graphically presents the change inconductivity over time for DBU/1-hexanol in toluene in the presence ofN₂.

FIG. 15 graphically presents conductivity of neat ethylbutylamine wherecarbon dioxide is added at room temperature (from 0 to 55 minutes), andwhere N₂ is added (from 55 to 100 minutes, 55° C.).

As described in the working examples, several ionic liquids have beenformed according to the invention by reacting carbon dioxide withamidines or guanidines and alcohols or water. An advantage of thealcohol system is that the reverse reactions are readily effected byremoving the carbon dioxide from the ionic liquid by flushing the systemwith a non-toxic gas that is substantially free of CO₂. The alcoholsystem is therefore advantageous to chemical processes whereinreversibility of the solvent switching is desirable. An advantage of thewater system is the rapid rate of reaction to form the bicarbonate ionicliquids from the nonionic liquids, perhaps due to a more favorablethermodynamic process. Due to this fast rate of reaction relative to thealcohol system, it is postulated that if a mixture of water and alcoholis used, the water will be used up prior to the consumption of thealcohol. This selectivity may have applications in industry in processeswhere it is desirable to remove water from solvents or other liquids. Ifthe quantity of reactant was known, this method may be useful forremoving water from alcohols as well. Similarly, consumption of alcoholin a solvent mixture to form a nonionic liquid as described may bedesirable.

Compounds of the invention may have higher aliphatic (C₅-C₂₀) and/orsiloxyl groups, however, higher aliphatic groups may cause a compound tobe waxy and non-liquid at room temperature. Preferred embodiments of theinvention are liquid at room temperature. Also, as the length of analiphatic and/or siloxyl group increases, the gap between the polaritiesof the solvent in its two states is diminished. For these reasons,preferred aliphatic and/or siloxyl chain length is 1 to 6. A siloxylgroup contains {—Si(R⁶)₂—O—} units, where R⁶ is preferably a substitutedor unsubstituted alkyl, aryl (including heteroaryl), or alkoxy moiety.(Other possible substitutents are listed below.) Conveniently, in somediscussions herein, the term “aliphatic/siloxyl” is used as shorthand toencompass aliphatic, siloxyl, and a chain which is a combination ofhydrocarbon and siloxyl units. A compound having a group that includesan ether or ester moiety is also encompassed by the invention. Inpreferred embodiments, the aliphatic/siloxyl group is alkyl.Aliphatic/siloxyl groups may be substituted with one or more moietiessuch as, for example, a substituent is independently alkyl, alkenyl,alkynyl, aryl, aryl halide, heteroaryl, non-aromatic rings, Si(alkyl)₃,Si(alkoxy)₃, halo, alkoxy, amino, ester, amide, thioether,alkylcarbonate, phosphine, thioester, or a combination thereof. Reactivesubstituents such as alkyl halide, carboxylic acid, anhydride, aldehydeand acyl chloride are not preferred.

In other embodiments of the invention all of the R¹⁻⁵ groups of thecompounds of the invention are not higher aliphatic/siloxyl; they arelower aliphatic/silyl groups, and are preferably small, nonpolar andnon-reactive. Examples of such groups include lower alkyl (C₁ to C₄)groups. Preferred examples of the lower aliphatic/silyl groups are CH₃,CH₂CH₃, CH(CH₃)₂, C(CH₃)₃, Si(CH₃)₃, and phenyl. Monocyclic, or bicyclicring structures, such as, for example, DBU, are also preferred.

In certain embodiments, the amidine or guanidine does not have any N—Hbonds. In preferred embodiments, conversion of the liquid mixture to anionic liquid is complete. In certain embodiments, the conversion toionic liquid is not complete; however, a sufficient amount of the liquidmixture is converted to the ionic liquid form to change the propertiesof the liquid. Analogously, in some embodiments, the conversion of ionicliquid back to the nonionic liquid may not be complete; however asufficient amount of the ionic liquid is converted to the nonionicliquid mixture to cause a useful change in the properties of the liquid.

In other embodiments, an amidine moiety (or guanidine moiety or othernitrogen-containing organic moiety) is present within the same moleculeas an alcohol moiety, such that the molecule converts into azwitterionic species in the presence of CO₂. Preferably, thezwitterionic form of the compound converts back to its uncharged formwhen the CO₂ is removed. A chemical scheme depicting the formation of azwitterionic ionic liquid is depicted below, where B represents anorganic basic moiety such as amidine or guanidine and where the curvedline represents portions of the molecule between the basic moiety andthe alcohol moiety.

It should be understood that the invention further encompasses acombination of amidines, a combination of guanidines, and a combinationof amidines and guanidines that react to form ionic liquids in thepresence of water or alcohol, or a combination thereof, and in thepresence of CO₂, CS₂, COS, or a combination thereof, as discussedherein. Similarly, a combination of nitrogen-containing organiccompounds, with or without amidines, guanidines or amines, are alsoincluded in the invention.

Preferably, the choice of alcohol should complement the amidine orguanidine being used in each system. Alcohols that were tested in asystem of DBU and CO₂ were 1-propanol, 1-butanol, 1-hexanol, 1-octanol,2-octanol, 1-decanol, and phenol (see Example 1). Certain of thesesystems (e.g., 1-propanol, 1-butanol, phenol) formed viscous ionicliquids at room temperature. Miscibility data for the ionic liquids withtraditional nonpolar solvents is presented in Table 1. The ionic liquidswere thoroughly characterized spectroscopically by NMR and the NMR datais presented in Tables 2 and 4. Analogous data for unreacted alcohols ispresented in Tables 3 and 5 for ease of comparison. Results ofconductivity studies of neat DBU/1-hexanol and neat DBU/1-tert-butanolduring CO₂ bubbling are presented in FIGS. 12A and 12B. The ionicliquids prepared from 1-hexanol, 1-octanol and 1-decanol appeared liquidat room temperature upon preparation. However, subsequent melting pointtests (by freezing and thawing samples) showed their melting points tobe slightly above room temperature (see FIG. 3). In contrast, the saltsprepared by the reaction of CO₂ with an equimolar mixture of DBU andwater (Perez, 2004; Hon et al., 1986; Heldebrant et al., 2005), DBU andmethanol (Main, 2001; Munshi, 2002) and DBU and ethanol were reported tohave formed white solids at room temperature (T_(dec) was 104-108° C.for bicarbonate). In addition, 3-ethyl-3-pentanol, a tertiary alcohol,did not react with CO₂ and DBU, either in neat form or in CDCl₃.

Exposure of a 1:1 mixture of the two miscible nonionic liquids, DBU and1-hexanol, to gaseous CO₂, at 1 atmosphere, caused a conversion to anionic liquid having a melting temperature slightly above roomtemperature (see FIG. 1 for the chemical scheme and Example 1 forprocedural details). This exothermic reaction caused a marked increasein the viscosity of the resultant liquid. NMR data for the n-hexanol/DBUsystem is presented in Table 6. The detection of the hexylcarbonateanion was confirmed by mass spectroscopy as described in Example 1A. Theionic liquid was converted back into a nonionic liquid by bubbling argonthrough the liquid at room temperature. The same reaction was alsoperformed at 50° C.; it occurred more rapidly at the higher temperature.

Conversion between a nonionic liquid and an ionic liquid results in achange in the properties of the solvent. As depicted in FIG. 4, thenonionic liquid mixture of 1-hexanol and DBU under N₂ was miscible withdecane, which is a nonpolar solvent. The ionic liquid that was formedfrom 1-hexanol/DBU/CO₂ was immiscible with decane (see Table 1). ThusCO₂ and N₂ at 1 bar can be used as triggers of immiscibility andmiscibility, respectively. Equimolar mixtures of DBU with 1-butanol,1-hexanol and 1-octanol exhibited the same behaviour with hexane as wasdescribed above for decane. The nonionic forms (while under N₂) weremiscible. The ionic forms (while under CO₂) were immiscible. However,miscibility was restored when N₂ was bubbled through the mixtures. Bycontrast, a 1:1 mixture of DBU and 1-decanol was miscible with hexaneeven when exposed to CO₂. In this case, the relatively low polarity ofthe ionic form, due to the length of the decyl chain in the alcohol,caused the ionic form to be sufficiently nonpolar so as to be misciblewith hexane.

Switchable solvents are useful for extraction of a solute from amixture, a solution, or a matrix. After extraction, the switchablesolvent is triggered to switch to its other form, to cause theprecipitation or separation of the solute from the solvent. The solventcould then be re-used. Solutes for extraction are either pure compoundsor mixtures of compounds. They include both contaminants and desiredmaterials. Such solutes can be extracted from various compositions,including, without limitation, soil, clothes, rock, biological material(for example, wood, pulp, paper, beans, seeds, meat, fat, bark, grass,crops, fur, natural fibres, cornstalks, oils), water, equipment, ormanufactured materials (for example, machined parts, molded parts,extruded material, chemical products, refined oils, refined fuels,fabrics, fibres, sheets, and like materials, whether made of metal,mineral, plastic, inorganic, organic, or natural materials orcombinations thereof). Desired solutes to be extracted include, withoutlimitation, medicinal compounds, organic compounds, intermediatecompounds, minerals, synthetic reagents, oils, sugars, foods,flavorants, fragrances, dyes, pesticides, fungicides, fuels, spices, andlike materials.

Studies were conducted on the effect of polarity on solubility of solidsolutes in ionic and nonionic forms of a DBU/1-propanol mixture. Forsolid solutes, 50 mg of solute were added to 2.22 mL of switchablesolvent mixture. The mixtures were then hand shaken and solubility wasdetermined qualitatively. Results are presented in Tables 14 and 15 andindicate that switchable solvents are particularly suitable forseparation of solutes such as, for example, decane, tetracosane,polystyrene, stilbene, glucose and [PhCH₂NEt₃]Cl, since these substanceswere soluble or miscible in one of the ionic or nonionic forms but notin the other form. Solutes that could react with either amidine oralcohol are not suitable for dissolution in amidine/alcohol mixtures;such solutes may be, for example, acids, strong bases and alkyl halides.

A study of the suitability of switchable solvents for use as a medium inwhich to synthesize polymer was conducted using styrene. Details areprovided in Example 10. A system of DBU and 1-propanol was used in itsnonionic form for synthesis of polymer and then switched to ionic formfor isolation of the polymeric product. A monomer, styrene and aninitiator, K₂S₂O₈, were added to the nonionic solvent mixture undernitrogen. The reaction was allowed to proceed and a solution of polymerwas obtained. Isolating polymer from traditional solvent is difficult,since the product is typically so fine that it clogs up a filteringapparatus. In this case, when the switchable solvent was switched to itsviscous ionic form and was diluted (optional) with a non reactivesolvent, 1-propanol, polymer particles precipitated from solution andwere easily filtered. Since switchable solvents have two distinct setsof physical properties that can be switched from one set to the otherset by a trigger, they are well suited to assist with isolating solutesthat are difficult to isolate using traditional solvents.

The CO₂/N₂ switchable system of an equimolar mixture of DBU with ethanolexhibited different behaviour from the higher alkylcarbonates discussedabove. The amidinium ethylcarbonate was immiscible with hexane, tolueneand ethyl acetate, and formed a separate liquid phase even though it issolid when pure. It is not yet understood whether this is supercoolingbehaviour or a melting point depression due to the presence of the extrasolvent. The polarity of liquid [DBUH][O₂COEt] is far higher than thatof liquid [DBUH][O₂COC₆H₁₃].

The polarity of the 1-hexanol/DBU 1:1 mixture was measured with the useof two solvatochromic dyes, Reichardt's dye (a pyridinium N-phenolatebetaine also known as E_(T)(30)) (Reichardt, 2003) and Nile Red.Reichardt's dye was green when dissolved in the alcohol/DBU mixturesunder N₂ and appeared yellow when dissolved in the same liquids underCO₂. This colour change is likely due at least partly to protonation ofthe dye or hydrogen-bonding of the dye with the acidic proton ofprotonated DBU or carbonic acid monohexylester; for this reason use ofReichardt's dye was discontinued in this study.

Ionic solvents were made from reacting DBU and C3 to C10 alcohols withcarbon dioxide. The polarities of the resultant ionic liquids arerepresented by the wavelength of maximum absorbance of light of Nile Reddissolved in the ionic liquids presented in FIG. 2 (upper curve).Similarly, the polarities of the equimolar DBU/alcohol mixtures under N₂are represented by the lower line in FIG. 2.

The melting point of the DBU/alcohol/CO₂ ionic liquids as a function ofthe alcohol's chain length are depicted graphically in FIG. 3. Thisgraph shows that for room temperature applications of the switchablesolvent of the invention, a carbon chain length of 3 to 6 is preferredto avoid freezing of the ionic liquid. A carbon chain length of 3 to 5is particularly preferred for this reason. It is noted that a pure ionicliquid of carbon length of 6 is prone to freeze at approximately 22° C.

The switchable solvents that use water rather than alcohol as the secondcomponent of the nonionic form differ from the switchable solvents thatuse alcohol because the amidines, guanidines or other N-containingorganic bases are usually but not necessarily immiscible with water.Thus in most cases the nonionic form of a base/water mixture wouldconsist of two phases, one organic and one aqueous, and would merge to asingle ionic liquid phase upon exposure to CO₂. If the melting point ofthe bicarbonate salt thus produced is above room temperature, and alower melting point is desired, then the molar ratio of water to base inthe original mixture is preferably greater than 1 or less than 1. Thismiscibility behaviour is observed in the systems described in theN,N,N′,N′-tetramethyl-N″-phenylguanidine andN,N,N′,N′-tetramethyl-N″-(2-fluorophenyl)guanidine schemes of FIG. 5. Incontrast, most base/alcohol pairs and some base/water pairs formmiscible mixtures even in their nonionic forms.

The particular choice of alcohol for use with the invention depends onthe amidine or guanidine compound. In the case of DBU, methanol andethanol are not preferred when it is desired to obtain a liquid at roomtemperature. In contrast, propanol or a higher alcohol are suitable forDBU.

In certain embodiments of the invention, a combination of two or morealcohols is used in place of a single alcohol. In some embodiments itmay be preferably to have multicomponent mixtures to decrease themelting point of the resultant ionic liquid and/or modify otherproperties of the ionic or nonionic forms of the switchable solvent. Insome embodiments of the invention, ionic liquids or nonionic liquidmixtures are added to conventional solvent(s) in either form. Advantagesof adding conventional solvents to switchable solvents include increasedspeed of switching, less viscous mixtures and maintenance ofconductivity. A study comparing the conductivity of DBU and 1-propanolversus DBU, 1-propanol and tetrahydrofuran is presented in FIG. 13.Results of a conductivity study of DBU, 1-hexanol and toluene are shownin FIGS. 14A and 14B.

In some embodiments, the ratio of non-gaseous reactants (amidine orguanidine or similar base and alcohol, water or alcohol/water mixture)is about equimolar. This is advantageous since when the ionic liquid isprepared from this mixture, there will remain little or no unreactedreactant(s) and the change in physical properties upon switching will bemaximized.

In other embodiments, the ratio of non-gaseous reactants is notequimolar. As a result, when the ionic liquid is formed, it is presentwith a reactant. This situation may be advantageous, for example it maylower the melting point.

In other embodiments, carbon dioxide may be replaced by substitute gasescarbon disulfide (CS₂) or carbonyl sulfide (COS). Carbonyl sulfide isnot preferred because of its flammability, its negative impact on humanhealth (irritant, damage to nervous system), and its negative impact onthe environment. Carbon disulfide is not preferred because of itsflammability, its toxicity, and its negative impact on the environment.Nevertheless, CS₂ and COS are expected to be capable of triggering thesame change in the switchable solvents as can CO₂.

Carbon dioxide may be provided from any convenient source, for example,a vessel of compressed CO₂(g) or as a product of a non-interferingchemical reaction. The ionic liquid can be converted to a nonionicliquid by removing the carbon dioxide, for example, by exposing themixture to a gas that contains insufficient CO₂ to sustain the ionicform, e.g., a gas that contains substantially no carbon dioxide.Preferably, the gas is non-toxic. Preferred gases that are substantiallyfree of CO₂ include, for example, argon, N₂, argon, air that hasinsufficient carbon dioxide to switch the nonionic liquid mixture toionic liquid, and air with the carbon dioxide component removed. In someembodiments, dried air, without any removal of the existing CO₂ content,will suffice. In some cases, normal air, without any removal of eitherthe existing CO₂ or the H₂O content, will suffice. Conveniently, suchexposure is achieved by bubbling the gas through the mixture or by anyother means of providing efficient contact between the liquid and gasphases. However, it is important to recognize that heating the mixtureis an alternative method of driving off the CO₂, and this method ofconverting the ionic liquid to nonionic liquid is also encompassed bythe invention. In certain situations, especially if speed is desired,both bubbling (or other means of providing efficient contact) and heatcan be employed. Heat may be supplied from an external heat source,preheated nonreactive gas, exothermic dissolution of gas in the liquidphase, or an exothermic process or reaction occurring inside the liquid.

Some embodiments of the invention require a pressure of CO₂ greater than1 bar to switch the solvent from nonionic to ionic. Preferredembodiments are able to react with CO₂ at 1 bar or less to trigger theswitch. High pressure switchable solvents require a pressure of CO₂greater than 1 atm to switch to ionic form and are substantially.completely switched to the nonionic form by a decrease in CO₂ pressureto about 1 atm. High pressure switchable solvents may be more timeefficient than atmospheric-pressure systems. These high pressureswitchable solvents may differ from the atmospheric-pressure switchablesolvents by a change in the steric or electronic properties of the aminebase (e.g., guanidine or amidine). Such molecules may include, forexample, tertiary amines, such as N-methylpyrrolidine, and amidines andguanidines with decreased basicity when compared to DBU such as amidinesand guanidines having aryl groups directly attached to one or more ofthe N atoms. Alternatively, high pressure switchable solvents may differfrom the atmospheric pressure switchable solvents by a change in thesteric or electronic properties of the alcohol. It should be understoodthat the invention encompasses amidine or guanidine compounds that havelower or about equal basicities than DBU and that react with CO₂ in thepresence of alcohol, water or a combination thereof under high pressure(i.e., are high pressure switchable solvent compounds).

1-methylpyrrolidine and 1-pentanol were tested at high pressure CO₂; adecrease in polarity from 526 nm to 511 nm was observed at 57 bar CO₂.DBU and 2-butanol were studied at high pressure CO₂; an increasedviscosity and slightly lowered polarity were observed relative to low.pressure CO₂. DBU and 2-propanol were studied at high pressure CO₂; anincreased polarity (546 nm) was observed relative to low pressure CO₂(541 nm).

Although the requirement for high pressure in generation of an ionicliquid can be viewed as a disadvantage, the ability to switch theproperties of such a molecule rapidly by reduction of the CO₂ pressuremay conversely be viewed as an advantage. For these reasons, the highpressure switchable solvents may be particularly suited to someindustrial processes, for example, where elevated pressures are alreadyused or where rapid solvent switching is required.

Atmospheric pressure switchable solvents include amidines, guanidinesand primary and secondary amines, each with aliphatic/siloxyl portion(s)as discussed below. If the switch to the ionic form is to be easilyreversible, the amidines or guanidines are preferably peralkylated. Theterm “peralkylated” as used herein means that the amidine or guanidinehas alkyl or other groups connected to the N atoms so that the neutralmolecule contains no N—H bonds. This lack of N—H groups is intended toavoid potentially irreversible reactions with carbon dioxide. If theswitch to the ionic form is not to be reversible, then there is nopreference that the amidine or guanidine be “peralkylated”.

An alternative method of preparing a high-pressure switchable solventwould be to use an alcohol that shows diminished conversion to the alkylcarbonate (in the presence of an amidine or guanidine and carbondioxide) at 1 atm of CO₂ pressure. An example of such an alcohol is asecondary or tertiary alcohol.

An advantage of switchable solvents is that they facilitate organicsyntheses and separations by eliminating the need to remove and replacesolvents after each reaction or separation step, e.g., when a solventwith different physical properties is needed. With triggers that arecapable of causing a drastic change in the solvent properties while itis still in the reaction vessel, it may be possible to use the samesolvent for two or more consecutive reaction or separation steps. Thiswould eliminate the need to remove and replace the solvent.

Reuse and recycling of solvents of the invention are convenient, withattendant economic benefits. The time required to switch between theionic and nonionic forms according to the invention is short. In certainapplications, it may be advantageous to convert from nonionic to ionicand then back again (or vice-versa). For example, the solvent could bemade nonionic to be miscible with a nonpolar liquid, and then thesolvent could be switched to its ionic form to allow for separation ofthe resulting two liquid components. The liquid components may or maynot appear as distinct layers. Separation of the components may includedecanting, or centrifuging. After separation, it may be desirable toconvert the ionic form back to its nonionic form. Thus the solvent canbe reused. In some embodiments it may be desirable to use the solvent inits ionic form. This molten salt form would separate from aqueoussolutions when converted to its nonionic form, allowing for easyrecovery and reuse of the solvent.

The invention provides a convenient system to controlling the propertiesof a solvent. Thus, it is useful in many industrial applications. Forexample, a chemical reaction that requires a polar solvent could beperformed in the switchable solvent while in its ionic form. Once thereaction is complete, the solvent could be switched to its nonionic formwhich is substantially incapable of dissolving the product of thereaction. This would force the product to precipitate, if solid, orbecome immiscible, if liquid. The solvent could then be separated fromthe product by physical means such as, for example, filtration ordecantation. If appropriate, the solvent could then be switched back toits ionic form and reused. This method allows the use of a polar solventwithout the requirement for an energy-intensive distillation step toremove the solvent. Such distillation steps are costly since many polarsolvents have high boiling temperatures.

A switchable solvent would be advantageous in a two-step chemicalsynthesis in which the first step requires a polar solvent and thesecond step requires a nonpolar solvent (or vice versa). The firstchemical reaction, which requires a polar solvent, could be performed inthe solvent while in its ionic form, producing a chemical intermediate.Once the first reaction is complete, the solvent could be switched toits nonionic form, which is capable of maintaining the chemicalintermediate in solution. The intermediate would then be converted to adesired product by a second reaction, which requires a nonpolar solvent.Traditionally, this two-step synthesis would be performed using twosolvents, a polar solvent for the first step, and a nonpolar solvent forthe second step. The removal of the polar solvent after the end of thefirst step would involve extra cost, time and energy. Thus switchablesolvents as described herein can lessen the financial and environmentalcosts of industrial processes, by saving time and energy normallyexpended during solvent substitutions, or during solvent removal fromproduct or solute.

Switchable solvents of the invention can be useful in water/solvent oralcohol/solvent separations in biphasic chemical reactions. As seen inFIG. 4, separation of a nonionic liquid from a switchable solvent may beeffected by switching the switchable solvent to its ionic form. Thisability to separate a liquid from a solvent may be useful in manyindustrial processes where upon completion of a reaction, one of thesolvents is switched to its ionic form allowing for facile separation ofthe two distinct phases. Thus a switchable solvent, may be used in itsnonionic state as a medium for a chemical reaction. Upon completion ofthe reaction, the chemical product is readily separated from solution byswitching the solvent to its ionic form. The solvent can then berecovered and reused, if appropriate.

A further aspect of the invention is a nonionic liquid mixture that islargely nonconductive (or only weakly conductive) of electricity, thatbecomes more conductive when it is converted to its ionic form, and thatthis change may be reversible. In the hexanol/DBU system described inExample 1A, conductivity of the ionic form was 20 times that of thenonionic form. A similar result can be seen in FIG. 10 for a guanidinesystem. Such a conductivity difference would enable the liquid to serveas an electrical switch, as a switchable medium, as a detector of CO₂,CS₂ or COS, or as a sensor of the presence of CO₂, CS₂ or COS. Thisability of the ionic liquid to conduct electricity can have applicationsin electrochemistry, in liquid switches and in sensors and/or detectors.Common, affordable CO₂ sensors are typically effective at 2-5% CO₂. CO₂sensors that work between 2-100% are usually large and prohibitivelyexpensive. A chemical approach based on switchable solvents can costmuch less.

Preliminary studies were conducted on use of the change in conductivityof DBU/ROH mixtures and of secondary amines for sensing CO₂ content ofgas mixtures. These studies are described in Examples 7 and 8. In bothsystems, inert solvent can be added for greater signal and fasterresponse. See FIGS. 13 and 14 for studies comparing neat systems tosystems with added inert solvents such as THF and toluene. In thesecondary amine system the solvent is preferably polar (e.g., DMSO orMeCN), rather than nonpolar (e.g., toluene).

Conveniently, a CO₂ sensor based on conductivity changes of a reversiblyswitchable solvent as described herein is effective in the range ofabout 5 to about 15% CO₂. For example, a thin film of neat DBU/1-hexanol(or other suitable amidine and/or guanidine/alcohol) can be used as aCO₂ sensor. The thin film allows for a shortened amount of time forswitching compared to the amount of time shown in FIG. 12 for switchingof a larger quantity of neat DBU/1-hexanol. Alternatively, mixing theamidine and/or guanidine/alcohol mixture with an inert solvent wouldshorten the amount of time for switching, as seen in FIG. 13.

WORKING EXAMPLES

DBU (Aldrich, Oakville, Ontario, Canada, 98% grade) was dried byrefluxing over CaH₂ and distilled under reduced pressure onto 4 Åmolecular sieves and then deoxygenated by repeated freeze/vacuum/thawcycles or by bubbling with carbon dioxide followed by filtration toremove any bicarbonate precipitate. Alcohols (99+%, anhydrous) were usedas received from Aldrich. Decane (Aldrich, 99+% grade) was degassed withnitrogen prior to use. Hexanes (Fisher Scientific, HPLC grade) andtoluene (Fisher Scientific, HPLC grade) were degassed and dried bypassing them through an activated alumina column under nitrogen prior touse. Ethyl acetate (Fisher Scientific, HPLC grade) was degassed withnitrogen prior to use. Supercritical grade CO₂ (99.999%, H₂O<0.5 ppm),nitrogen (99.998%, H₂O<3 ppm) and argon (99.998%, H₂O<5 ppm) were usedas received from Praxair Canada Inc., (Mississauga, Ontario, Canada).

Example 1 Reversible Solvent Switching in an Amidine and Alcohol SystemExample 1A Reversible Solvent Switching in a DBU and 1-Hexanol System

Dried DBU (0.60 mL, 4.0 mmol, see FIG. 1) and 1-hexanol (0.50 mL, 4.0mmol) were placed in a dry glass NMR (Nuclear Magnetic Resonance) tubein a glove box (Vacuum Atmospheres Company, Hawthorne, Calif.) under N₂.Carbon dioxide was bubbled through the liquid via a hollow narrow-gaugestainless steel tube which was inserted in the solution within the NMRtube. The rate of bubbling was 2 bubbles per second for 1 hour. Theliquid became increasingly viscous. The conductivity of a similarsolution was measured using an immersible conductivity probe (Jenway,model 4071, available at Canadawide Scientific, Ottawa, Canada); itincreased more than 20 fold. The ¹H NMR spectrum of the resultantsolution, although broadened due to the solution's viscosity, clearlyindicated complete conversion to [DBUH][O₂CO(CH₂)₅CH₃] (where “DBUH” isprotonated DBU) with no residual signals for free 1-hexanol orunprotonated DBU. The ¹H NMR resonance in CDCl₃ attributed to theoxygen-bound methylene of the hexyl group had shifted to 3.90 ppm from3.58 ppm (the resonance for the same methylene group in unreactedhexanol). This resonance is comparable to the corresponding chemicalshifts seen for CH₃C(O)O(CH₂)₅CH₃ (in CDCl₃) at 4.05 ppm (Reynders,1990) and dihexyl carbonate at 4.13 ppm (in CCI₄) (Sakai, 1971).

Please see the picture below for the numbering scheme for positions inthe DBU structure.

Spectroscopic data for [DBUH][O₂CO(CH₂)₅CH₃]:

¹H NMR (δ, ppm, in CDCl₃) 3.90 (t, 2H, hexyl C1), 3.49 (m, 4H, DBUH C2and C11), 3.43 (t, 2H, DBUH C9), 2.81 (br, 2H, DBUH C6), 2.00 (quintet,2H, DBUH C10), 1.75 (br, 6H, DBUH C3, C4, and C5), 1.58 (quintet, 2H,hexyl C2), 1.37 (m, 2H, hexyl C3), 1.29 (br, 4H, hexyl C4 and C5), 0.87(t, 3H, hexyl C6).

¹³C{¹H} NMR (δ, ppm, in CDCl₃, referenced to CDCl₃ at 77.2 ppm) 164.9(DBUH C7), 158.7 (O₂COR), 64.6 (hexyl C1), 53.5 (DBUH C2), 48.1 (DBUHC11), 38.6 (DBUH C9), 32.3 (DBUH C6), 31.5 (hexyl C4), 29.4 (hexyl C2);28.8 (DBUH C4), 26.8 (DBUH C3), 25.5 (hexyl C3), 24.0 (DBUH C5), 22.2(hexyl C5), 19.7 (DBUH C10), 13.7 (hexyl C6).

IR (neat) 2938 (m), 1648 (s), 1613 (s), 832 (m), 688 cm⁻¹ (m).

Mass Spectroscopy of a Mass Spectroscopy Sample in ElectrosprayIonization negative mode (“MS/MS (ESI, negative mode)” 145.1 (M), 101.1(M—CO₂), 99.1 (M—H₂CO₂), 83.0 (M—H₂CO₃), 60.0 (CO₃ ⁻), where “M” is theanion C₆H₁₃OCO₂ ⁻.

For comparison, literature shows that [NBu₄][O₂COEt] has a ¹³C{¹H} NMRsignal for the carbonyl at 157.9 ppm in CDCl₃ and IR peaks at 2940, 2880and 1670 cm⁻¹ in KBr (Verdecchia, 2002).

Spectroscopic changes upon exposure of the hexanol/DBU mixture to CO₂are presented in Tables 2, 4 and 6. Solvatochromic data measuring thepolarity of the liquid before and after exposure to CO₂ are presented inFIG. 2.

Reversability of the reaction was confirmed when a sample of the ionicliquid in an NMR tube was heated to 50° C. and argon was bubbled throughthe sample for 1 h. The viscosity dropped greatly. The ¹H NMR spectrumafter this procedure was consistent with the spectra of 1-hexanol andDBU, showing no peaks for residual ionic liquid.

Exposure of [DBUH][O₂COC₆H₁₃] ionic liquid to moist air resulted in theappearance of a white solid within a few minutes. The white solid,washed with acetonitrile, was identified as the bicarbonate salt[DBUH][O₂COH] by IR and ¹H NMR (in CDCl₃).

Example 1B Reversible Solvent Switching in Systems of DBU and VariousAlcohols

Analogous tests as the one described in Example 1A were performed forDBU and n-chain alcohols having 1, 2, 3, 4, 6, 8 and 10 carbon atoms.The products of the DBU with the C3-C10 alcohols were liquids at roomtemperature as indicated in FIG. 3. Preliminary tests of DBU withsecondary and tertiary alcohols were not successful in obtainingcomplete conversion to ionic liquids: An example of a tertiary alcohol,3-ethyl-3-pentanol, with an equimolar amount of DBU did not react withcarbon dioxide. Secondary alcohols (2-octanol, (1R, 2S, 5R)-(−)-mentholand (1S)-endo-(−) borneol) reacted to form an ionic liquid, but completeconversion was not obtained. The greatest conversion of these-secondaryalcohols (about 64%) was obtained with 2-octanol.

In the cases of the primary n-alcohols, the ionic liquids werecharacterized by ¹H and ¹³C NMR spectroscopy. The reversibility of thereaction in each case to reform DBU and the appropriate alcohol was alsoconfirmed by ¹H NMR. Spectroscopic changes upon exposure of thealcohol/DBU mixtures to CO₂ are presented in Tables 2, and 4 while theunreacted alcohols' spectroscopic data is presented in Tables 3 and 5,for comparison purposes.

Solvatochromic data measuring the relative polarities of the DBU/alcoholmixtures before exposure to CO₂ and the corresponding ionic liquidsafter exposure to CO₂ are presented graphically in FIG. 2, where the yaxis is the wavelength of the peak of Nile Red dye in the solvent. Highpolarity is represented by a greater wavelength value, and lowerpolarity is represented by a lower wavelength value.

The melting point of the ionic form of the switchable solvent made fromDBU and an alcohol having 1 to 10 carbon atoms is presented graphicallyin FIG. 3 wherein the y axis is the melting point and the x axis is thelength of carbon chain of the R component of the salt which is derivedfrom the alcohol.

Example 2 Miscibility Switching in a DBU and Alcohol System

In an inert atmosphere, 26.8 mmol each of DBU (95 ppm H₂O) and 1-hexanol(₂₆ ppm H₂O) were charged into a flame-dried flask. N-Decane (2 mL,undried) was added and was found to be miscible at room temperature;only one homogeneous liquid phase was observed. CO₂ (H₂O<5 ppm) wasslowly bubbled through the decane/1-hexanol/DBU mixture at 1 barovernight. The resultant mixture appeared split into two separateliquids. Argon was then bubbled through the two-phase liquid mixture for1 h at 35° C. After 1 h, the two liquids had merged into one liquid. Aschematic representation of this reversible reaction appears in FIG. 4.Similar experiments were performed with hexane in place of decane andwith several alcohols (1-propanol, 1-butanol, 1-hexanol, 1-octanol, and1-decanol) in place of 1-hexanol; similar results were obtained exceptthat with 1-decanol, no phase split was observed even after thetreatment with CO₂. Miscibility data for alcohol/DBU systems ispresented in Table 1.

Example 3 Guanidine and Water Systems Example 3A Solvent Switching inN,N,N′,N′-tetramethyl-N″-phenylguanidine Guanidine and Water Systems

An ionic liquid was reversibly formed by bubbling carbon dioxide througha solution of N,N,N′,N′-tetramethyl-N″-phenylguanidine (500 mg) (seeFIG. 5A) in wet diethyl ether (5 mL). The liquid bicarbonate salt formeda separate liquid phase from the diethyl ether (see FIG. 5C). The ionicliquid was characterized by ¹H NMR spectroscopy wherein the protonresonances of the guanidinium bicarbonate had shifted relative to thecorresponding resonances of the unreactedN,N,N′,N′-tetramethyl-N″-phenylguanidine (see FIG. 7).

Similarly, an ionic liquid was formed by bubbling carbon dioxide througha solution of N,N,N′,N′-tetramethyl-N″-(2-fluorophenyl)guanidine (500mg) (see FIG. 5B) dissolved in wet diethyl ether (5 mL). The liquidbicarbonate salt formed a separate liquid phase that was distinct fromthe diethyl ether as depicted in FIG. 5. The ionic liquid wascharacterized by ¹H NMR spectroscopy wherein the proton resonances ofthe guanidinium bicarbonate had shifted relative to the correspondingresonances of the unreactedN,N,N′,N′-tetramethyl-N″-(2-fluorophenyl)guanidine.

An ionic liquid was formed, in the absence of ether, by bubbling carbondioxide through an equimolar mixture of water andN,N,N′,N′-tetramethyl-N″-phenylguanidine. Prior to bubbling, the liquidsappear as a biphasic mixture with the guanidine on the top and the wateron the bottom. After bubbling, the liquid appeared as a single phaseionic liquid.

Attempts to reverse the switch to reform the nonionic guanidines ofExample 3 by bubbling the ionic liquids with argon have beenunsuccessful to date.

Example 3B Solvent Switching forN-phenyl-N′,N′,N″,N″-tetramethylguanidine (PhTMG) and Water

PhTMG (2 mL) and water (2 mL) were placed together in a small vial,forming a two-phase mixture. CO₂ was bubbled through the mixture for 2h, giving a single colourless viscous liquid phase, believed to be amixture of [PhTMGH][O₂COH] and water. ¹H and ¹³C NMR spectra of thisliquid in CD₃OD and that of the HCl salt of PhTMG in the same solventmatched, as seen below.

Characterization of the viscous liquid: ¹H NMR (CD₃OD) 3.0 (s, 12H, Me),7.1 (d, 2H, ortho), 7.2 (t, 1H, para), 7.4 ppm (t, 2H, meta). ¹³C NMR(CD₃OD) 39.9 (Me), 121.3 (ortho), 125.7 (para), 130.3 (meta), 138.8(N—C(arom)), 159.5 (N═C), 160.6 ppm (O₂COH).

PhTMG.HCl: ¹H NMR (CD₃OD) 3.0 (s, 12H, Me), 7.1 (d, 2H, ortho), 7.2 (t,1H, para), 7.5 ppm (t, 2H, meta). ¹³C NMR (CD₃OD) 40.8 (Me), 122.7(ortho), 127.3 (para), 131.8 (meta), 139.8 (N—C(arom)), 160.5 (N═C).

Example 4 Studies of Guanidine and Alcohol Systems Example 4A ReversibleSolvent Switching in Me-MTBD Guanidine and Alcohol System

An ionic liquid was reversibly formed by bubbling carbon dioxide througha mixture of 1,3,4,6,7,8-hexahydro-1-methyl-2H-pyrimido[1,2-a]pyrimidine(“Me-MTBD”, see FIG. 6A), which was used as purchased from Aldrich, and1-octanol. The formation of the ionic liquid was confirmed by ¹H NMRspectroscopy. The same reaction with methanol in place of octanol gave asolid product. Attempts to reverse the switch to reform Me-MTBD and1-octanol by heating the ionic liquids have been unsuccessful to date.

An ionic liquid was reversibly formed (as described in Example 1A) bybubbling carbon dioxide through a solution ofN,N,N′,N′-tetramethyl-N″-butylguanidine (see Example 5 and FIG. 6B) andmethanol. The formation of the ionic liquid was confirmed by ¹H and ¹³CNMR spectroscopy, including the ¹³C NMR technique known as “attachedproton test” (APT or DEPT). The reversibility of the reaction to reformthe nonionic guanidine and methanol was confirmed by ¹H and ¹³C NMR. Thereversal was achieved by bubbling N₂ through the neat ionic liquid at50° C. The reversal was also achieved by dissolving the ionic liquid ina solvent and then bubbling N₂ through that solution. The reversal bythe latter method, at room temperature, took 12 hours of bubbling inDMSO and greater than 24 hours in CDCl₃.

Example 4B Reversible Solvent Switching in2-butyl-1,1,3,3-tetramethylguanidine and Alcohol System

A reversibly switchable room temperature ionic liquid was formed byexposing an equimolar mixture of 2-butyl-1,1,3,3-tetramethylguanidine(Schuchardt et al. 1995; Cost et al. 1998) and methanol to gaseous CO₂at one atmosphere. Reversibility of this system was demonstrated by ¹Hand ¹³C NMR spectroscopy and conductivity studies (see FIGS. 9A-C, and10). Formation of the ionic liquid occurred after bubbling CO₂ for 20minutes through a 1:1 molar ratio mixture of2-butyl-1,1,3,3-tetramethylguanidine and methanol. The ionic liquid wasthen converted back to 2-butyl-1,1,3,3-tetramethylguanidine and methanolby bubbling the mixture with N₂ or argon overnight. The ionic liquid canalso be reversed solely by heat, as indicated by a thermogravimetricstudy (see FIG. 11 in which the ionic liquid underwent reversal,releasing CO₂ and low-boiling methanol at temperatures as low as 50°C.).

FIG. 9A shows an NMR spectrum of the initial equimolar solution of2-butyl-1,1,3,3-tetramethylguanidine and methanol. Upon the addition ofCO₂, protonation of the guanidine and formation of the methyl carbonateanion took place. This is evidenced in ¹H NMR by an upfield shift in thealiphatic protons, and the collapse of the two N—Me peaks into one peak(see FIG. 9B). Finally, FIG. 9C shows the ¹H NMR after nitrogen bubblingfor 16 hours. The ionic liquid has indeed reversed to its originalcomponents.

¹³C NMR spectra exhibited the appearance of a characteristic carbonatepeak at 161 ppm. Chemical shifts in the methoxyl and aliphatic carbons,and changes in N—Me peaks were clearly observed. Unreacted CO₂ was notdetected by ¹³C NMR as no peaks were present at 120 ppm.

Example 4C Conductivity Measurement of Methanol and2-butyl-1,1,3,3-tetramethylguanidine

The reversibility and repeatability of the conversion of an equimolarmixure of methanol and 2-butyl-1,1,3,3-tetramethylguanidine inchloroform to 2-butyl-1,1,3,3-tetramethylguanidinium methylcarbonatewere confirmed by a conductivity study. This study was conducted using aJENWAY conductivity meter 4071 (Jenway, Barloworld Scientific Ltd,Essex, England). When carbon dioxide was bubbled through the guanidineand alcohol mixture, the mixture changed from non-conducting (0-10μS/cm) to conducting (approximately 250 μS/cm) (see FIG. 10), indicatingthe formation of the ionic liquid 2-butyl-1,1,3,3-tetramethylguanidiniummethylcarbonate. The conductivity was then switched off by applying heat(80° C.) indicating the (re)formation of methanol and2-butyl-1,1,3,3-tetramethylguanidine. This cycle was repeated threetimes obtaining similar levels of conductivity each time.

Example 5 Thermogravimetric Analysis of2-butyl-1,1,3,3-tetramethylguanidinium Methylcarbonate

Thermogravimetric analysis (TGA) was used to determine the optimumtemperature for driving off carbon dioxide from a sample of2-butyl-1,1,3,3-tetramethylguanidinium methylcarbonate. The sample washeated in a TGA Q500 thermogravimetric analysis machine (TA Instruments,New Castle, Del., USA). See FIG. 11 for the resulting plot of heat flow,temperature and mass loss.

Example 6 Synthesis of N,N,N′,N′-tetramethyl-N″-butylguanidine

N,N,N′,N′-tetramethyl-N″-butylguanidine was prepared as follows: 9.3 gtetramethyl urea was added to 80 mL dry dichloroethane in a two-neck250mL round-bottom-flask. 11.3 mL oxalyl chloride was added and thesolution was heated at 70° C. for two hours. The solvent was evaporatedin vacuo after the solution cooled to room temperature. Residual solidwas then dissolved in dry acetonitrile and cooled to 0° C. 15 mL butylamine (1.02 eq) was slowly added. The solution was slowly warmed andallowed to reflux for one hour. Finally, the mixture was cooled to roomtemperature and the solvent was removed in vacuo to yield 9 g of a clearoil. ¹H (CDCl₃): δ(ppm): 2.99 (t, 2H); 2.62 (s, 3H); 2.53 (s, 3H); 1.39(quintet, 2H); 1.24 (quintet, 2H); 0.78 (t, 3H). The synthesis wasperformed several times and the yield ranged from 37%-70%.

Example 7 Studies of DBU/Alcohol System as CO₂ Sensor

The following experiments were conducted to study use of a DBU/alcoholsystem as a CO₂ sensor:

(1) CO₂ was bubbled through an anhydrous equimolar mixture of DBU and1-propanol at room temperature. After 30 minutes, the conductivity hadrisen from its initial value of 34 to values over 200 μS/cm; afterfurther bubbling for 2 h, the value rose to 300 μS/cm.

(2) CO₂ was bubbled through an anhydrous THF solution containing anequimolar mixture of DBU and 1-propanol at room temperature (1:1:3 moleratio DBU:ROH:THF). After 2 minutes, the conductivity rose from itsinitial value of 16 to 654 μS/cm, after which a steady drop inconductivity was observed. A loss in volume of the liquid was observedduring this drop in conductivity, indicating that at least one of thecomponents of the liquid mixture was being lost by evaporation. Therapid initial rise in conductivity indicates that the addition of aninert solvent (THF in this case) increased the rate of response of theconductivity to the presence of CO₂ and also increased the intensity ofthe signal (the magnitude of the conductivity). The inert solvent alsoreduced the cost of the method because THF is cheaper than DBU. The lossof liquid indicates that it would be better to use less volatileliquids.

(3) CO₂ was bubbled through an anhydrous toluene solution of anequimolar mixture of DBU and 1-hexanol at room temperature (1:1:3DBU:ROH:toluene mole ratio). The conductivity rose from below thedetection limit of the instrument up to a steady value of 285 μS/cm.This steady conductivity was reached after about 15 minutes. Flushing N₂through the mixture at room temperature caused the conductivity to dropto 5-6 μS/cm after 75 min. Bubbling CO₂ through the solution againcaused the conductivity to rise again, reaching a conductivity of269-275 μS/cm after 15 min.

Results of these studies indicate that using nonvolatile componentseliminates the conductivity drop seen in experiment (2); the reactioncan be reversed without the use of heat, and the conductivity isreproducible.

Example 8 Studies of Secondary Amines Example 8A Polarity Studies ofSecondary Amines

Each secondary amine (3 mL) was placed in a 1 cm glass cuvette. NileRed, a solvatochromatic dye, was added by syringe at which time thetransparent sample turned red. UV measurements were taken of thisnonionic form. Each sample was then sealed with an airtight septum andbubbled with carbon dioxide from a pressurized vessel for approximately20 minutes or until the heat of reaction subsided. UV measurements(λ_(max)) were taken again. Each sample was then switched back tononionic form by bubbling nitrogen gas into the cuvette and heating thecuvette in a 55° C.-60° C. oil bath for up to 2.5 hours. Periodic UVmeasurements were taken to determine the λ_(max). This was done untilthe λ_(max) was the same as the original nonionic form. Experiments wereperformed twice for each amine and average values appear in Table 12.

Example 8B Solubility and Miscibility Studies of NHEtBu

Substrate (50 mg) and ethylbutylamine (3.0 mL) were stirred together ina vial with septum under N₂. Whether the solid had completely dissolvedwas determined visually. CO₂ was bubbled through the solution for 30minutes with stirring, and a visual observation of phase behaviour wasconducted again. If there was a change in the phase behaviour, the vialwas heated to 50° C. and N₂ was bubbled through the solution for 2 h tosee if the change was reversible. For all cases that demonstrated achange, the change was reversible, with the exception of glucose.Glucose was insoluble before treatment with CO₂, soluble after CO₂treatment, and remained soluble after the N₂ treatment. Solubilityresults are presented in Table 14.

The miscibility of liquids was tested in a similar manner except thatthe amount of the liquid substrate was 0.5 mL. Miscibility results arepresented in Table 13.

Example 8C NMR Studies of Secondary Amines

NMR spectra of carbamate salts of secondary amines in CDCl₃ wereobtained in the following manner. Standard NMR tubes were filled toapproximately 5 cm with deuterated chloroform. 2-3 drops of a secondaryamine were added to the tube. An airtight septum was inserted into thetop of the tube and carbon dioxide was slowly bubbled through thesolution until the heat subsided. NMR results are reported in Tables 7and 8.

Example 8D Studies of NHEtBu System as CO₂ Sensor

The following experiments were conducted to study use of a NHEtBu systemas a CO₂ sensor:

1) Neat NHEtBu at room temperature (0 μS/cm) was bubbled with CO₂ andhad a conductivity of 0.67 μS/cm.

2) NHEtBu in MeCN (1:6 mol/mol) at room temperature had an initialconductivity of 6-12 μS/cm. CO₂ was bubbled through the solution for 5min and the conductivity rose to 140 μS/cm.

3) NHEtBu in toluene (1:6 mol/mol) at room temperature had an initialconductivity of 0 μS/cm. CO₂ was bubbled through the solution for 30minutes and the conductivity stayed at 0 μS/cm. Other amines (NHPrBu,NHMeBz) in toluene gave the same result

4) NHEtBu in DMSO (1:6 mol/mol) at room temperature had an initialconductivity of 6-15 μS/cm. CO₂ was bubbled through the solution for 5minutes and the conductivity rose to 500 μS/cm.

Example 9 X-Ray Crystallographic Study of [DBUH][O₂COMe]

A crystal of [DBUH][O₂COMe] (colorless, plate-shaped, size0.35×0.25×0.08 mm) was mounted on a glass fiber with grease and cooledto −93° C. in a stream of nitrogen gas controlled with a CryostreamController 700. Data collection was performed on a Bruker SMART CCD 1000X-ray diffractometer (Bruker BioSpin Ltd., Milton, Ontario, Canada) withgraphite-monochromated Mo K_(α) radiation (λ=0.71073 Å), operating at 50kV and 30 mA over 2θ ranges of 4.52˜50.00°. No significant decay wasobserved during the data collection. Data were processed on a Pentium PCusing the Bruker AXS Crystal Structure Analysis Package, Version 5.10.

Example 10 Synthesis of Polystyrene in Nonionic DBU/1-propanol andFacile Collection in Ionic DBU/1-propanol

DBU (3.0 mL) and 1-propanol (3.6 mL) (1:2.5 mol/mol) were placed in a2-necked flask under an N₂ atmosphere. K₂S₂O₈ (50 mg) was added followedby 2.0 mL of distilled styrene. The flask was stirred with a condenserattached for 12 hours at 50° C. After the polymerization reactionforming polystyrene was complete, the solution appeared clear andyellow, and no precipitate was visible. CO₂ was bubbled through thesolution for 1 hour to convert the solvent to its ionic form. 1-propanol(1.5 mL) was added to decrease the viscosity. Polystyrene precipitatedout of the ionic liquid and was filtered in an air-free Schlenk filterunder N₂. This completed the first cycle. The collected polystyrene waswashed with cold MeOH and characterized.

To the recycled solvent, DBU (0.6 mL) and distilled styrene (1.0 mL)were added, followed by K₂S₂O₈ (25 mg). The reaction was allowed toproceed for 12 hours at 50° C. CO₂ was bubbled through the solution for1 hour to convert the solvent to its ionic form and 1.5 mL of 1-propanolwas added to decrease the viscosity. Polystyrene precipitated and wasfiltered and characterized. This completed the second cycle. The samemethod was repeated for third and fourth cycles (i.e., each time addingpropanol, then adding the corresponding DBU quantity, to restore theirinitial molar ratio). The solvent was yellow for each cycle after thefirst.

Information regarding switchable solvents appears in Jessop, P. G.;Heldebrant, D. J.; Li, X.; Eckert, C. A.; Liotta, C. L. “A ReversibleIonic/Non-Ionic Switchable Solvent,” Nature 436, 1102 (2005), which ishereby incorporated in its entirety by reference. Furthermore, allscientific and patent publications cited herein are hereby incorporatedin their entirety by reference.

It will be understood by those skilled in the art that this descriptionis made with reference to the preferred embodiments and that it ispossible to make other embodiments employing the principles of theinvention which fall within its spirit and scope as defined by theclaims appended hereto.

References

Aki, S. N. V. K.; Brennecke, J. F.; Samanta, A., “How polar areroom-temperature ionic liquids?” Chem. Commun. 413-414 (2001).Carmichael, A. J. & Seddon, K. R. “Polarity study of some1-alkyl-3-methylimidazolium ambient-temperature ionic liquids with thesolvatochromic dye, Nile Red.” J. Phys. Org. Chem. 13, 591-595 (2000).Cost, M.; Chiusoli, G. P.; Taffurelli D.; Dalmonego, G.; “Superbasecatalysis of oxazolidin-2-one ring formation from carbon dioxide andprop-2-yn-1-amines under homogeneous or heterogeneous conditions.” J.Chem. Soc., Perkin Trans. 1, (1998) 9:1541-1546.Deye, J. F.; Berger, T. A.; Anderson, A. G. “Nile Red as solvatochromicdye for measuring solvent strength in normal liquids and mixtures ofnormal liquids with supercritical fluids and near critical fluids.”Anal. Chem. 62, 615-622 (1990).Jessop, P. G.; Leitner, W., Chemical Synthesis using SupercriticalFluids. VCH/Wiley: Weinheim, Germany (1999).Jen, W. S.; Wiener, J. J. M.; MacMillan, D. W. C. “New strategies fororganic catalysis: The first enantioselective organocatalytic1,3-dipolar cycloaddition” J. Am. Chem. Soc. (2000) 122(40): 9874-9875.Jessop, P. G.; Heldebrant, D. J.; Li, X.; Eckert, C. A.; Liotta, C. L. “A reversible ionic/non-ionic switchable solvent,” Nature 436, 1102(2005).Hori, Y.; Nagano, Y.; Nakau, J.; Taniguchi, H. “New method of organicsynthesis using DBU (6th report) Reversible Immobilization of CarbonDioxide Gas by Forming Carbonate, Carbamate Salt.” Kinki ChemicalSociety, Japan, Chemistry Express 1(3): 173-176 (1986).Main, A. D.; Fryxell, G. E.; Linehan, J., “Simple preparation of organicsalts of alkyl carbonates: an alternate synthesis of dimethylcarbonate”, unpublished material (2001).Muldoon, M. J., Gordon, C. M. & Dunkin, I. R. “Investigations ofsolvent-solute interactions in room temperature ionic liquids usingsolvatochromic dyes.” J. Chem. Soc.-Perkin Trans. 2, 433-435 (2001).Munshi, P.; Main, A. D.; Linehan, J.; Tai, C. C.; Jessop, P. G.,“Hydrogenation of carbon dioxide catalysed by rutheniumtrimethylphosphine complexes: the accelerating effect of certainalcohols and amines.” J. Am. Chem. Soc. 124, 7963-7971 (2002).Perez, E. R.; Santos, R. H. A.; Gambardella, M. T. P.; de Macedo, L. G.M.; Rodrigues-Filho, U. P.; Launay, J.-C.; Franco, D. W., “Activation ofcarbon dioxide by bicyclic amidines”. J. Org. Chem. 69, 8005-8011(2004).Reichardt, C. “Solvatochromic dyes as solvent polarity indicators.”Chem. Rev. 94, 2319-2358 (1994).Reichardt, C. “Polarity of ionic liquids determined empirically by meansof solvatochromic pyridinium N-phenolate betaine dyes,” Green Chem. 7,339-351 (2005).Reynders, P., Kuehnle, W. & Zachariasse, K. A. “Ground-state dimers inexcimer-forming bichromophoric molecules. 1.Bis(pyrenylcarboxy)alkanes.” J. Am. Chem. Soc. 112, 3929-3939 (1990).Sakai, S., Kobayashi, Y. & Isii, Y. “Reaction of dialkyltin dialkoxideswith carbon disulfide at higher temperature. Preparation oforthocarbonates.” J. Org. Chem. 36, 1176-1180 (1971).Subramaniam, B.; Busch, D. H., “Use of dense-phase carbon dioxide incatalysis”, Carbon Dioxide Conversion and Utilization, Song, C.;Gaffney, A. F.; Fujimoto, K., Eds. ACS: Washington, pp 364-386 (2002).Schuchardt, U.; Vargas R. M.; Gelbard, G.; “Alkylguanidines as catalystsfor the transesterification of rapeseed oil” J. Mol Cat A: Chem, 99: 65(1995).Verdecchia, M., Feroci, M., Palombi, L. & Rossi, L. “A safe and mildsynthesis of organic carbonates from alkyl halides andtetrabutylammonium alkyl carbonates.” J. Org. Chem. 67, 8287-8289(2002).Yamada, T.; Lukac, P. J.; George, M.; Weiss, R. G. “Reversible,room-temperature ionic liquids, amidinium carbamates derived fromamidines and aliphatic primary amines with carbon dioxide.” Chem. Mater.19: 967-969 (2007).

1. An ionic liquid of formula (2)

where R is alkyl, alkenyl, alkynyl, aryl, silyl, or siloxyl, and may belinear, branched, or cyclic, and may be substituted or unsubstituted;R¹, R², R³, and R⁴ are independently H; a substituted or unsubstitutedC₁ to C₁₀ alkyl group that is linear, branched, or cyclic; a substitutedor unsubstituted C_(n)Si_(m) group where n and m are independently anumber from 0 to 10 and n+m is a number from 1 to 10; a substituted orunsubstituted aryl group optionally containing one or more {—Si(R⁶)₂—O—}units; or a substituted or unsubstituted heteroaryl group optionallycontaining one or more {—Si(R⁶)₂—O—} units; and R⁶ is a substituted orunsubstituted alkyl, aryl, heteroaryl, or alkoxy moiety. 2-58.(canceled)